Magnetic Effect of Electric Current Class 10 Science Important Questions

Please refer to Magnetic Effect of Electric Current Class 10 Science Important Questions given below. These solved questions for Magnetic Effect of Electric Current have been prepared based on the latest CBSE, NCERT and KVS syllabus and books issued for the current academic year. We have provided important examination questions for Class 10 Science all chapters.

Class 10 Science Magnetic Effect of Electric Current Important Questions

Very Short Answer Type Questions :

Question.Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer:The direction of magnetic field will be perpendicular to the plane of paper inwards inside the loop and perpendicular to the plane of paper outwards from inside.

Question. What type of core is used to make electromagnets? 
OR
What type of core should be put inside a current-carrying solenoid to make an electromagnet?
Answer:Soft Iron

Question. Give the factors on which magnetic field produced by a current carrying solenoid will depend.
Answer:(i) The current through the solenoid. (ii) The number of turns in the solenoid
(iii) Nature of core on which wires are wound in solenoid.

Question. Name the factors on which force acting on a current carrying conductor will depend.
Answer:(i) The current through the conductor. (ii) The strength of magnetic field.
(iii) The length of the conductor.

Question. State the direction of magnetic field in the following case:

Answer:Direction is out of the page.

Question. A beam of alpha particles enters a chamber moving along the magnetic field. What is the magnetic force experienced by the beam?
Answer:Zero, it is because beam is moving parallel to the magnetic field.

Question. When is the force experienced by a current carrying conductor placed in a magnetic field greatest?
Answer:When the current in the conductor flows perpendicular (90°) to the direction of the magnetic field, maximum force is generated.

Question. What is the pattern of field lines inside a solenoid? What do they indicate? 
Answer:The magnetic field is in the form of parallel lines. It indicates a uniform magnetic field because magnetic field lines are parallel.

Question. How is magnetic field produced in a solenoid used? 
Answer:It is used to magnetise a soft iron bar to form an electromagnet.

Question. What does the direction of thumb indicate in the right hand thumb rule? 
Answer:The thumb indicates the direction of current in the straight conductor held by curved fingers of our hand.

Question. Suggest one way to distinguish a wire carrying current from a wire carrying no current.
Answer:The magnetic compass needle will get deflected near the wire current carrying but not near the wire with no current.

Question. Why are magnetic field lines form closed curves?
Answer:It is because outside the magnet, magnetic field lines start from north pole and merge at south pole whereas inside the magnet they start from south pole and merge at north pole, therefore these lines from closed curves.

Question. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer:The direction is vertically downwards.

Question. Which property of a proton will change while it moves freely in a magnetic field?
Answer: Momentum or Velocity.

Question. According to Flemings right hand rule, which part of right hand indicate the movement of conductor?
Answer: Thumb

Question. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer: As per right-hand rule, we find that inside the loop, the magnetic field lines are directed perpendicular to the plane of the paper in the inward direction. Outside the loop magnetic field lines are directed out of the plane paper.

Question. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer: The uniform magnetic field is represented by parallel equispaced lines of equal length as follows:

Question. What is the role of the split ring in an electric motor?
Answer: In electric motor, the split ring acts as commutator. Due to its action, the direction of current flowing in motor coil reverses after half turn, giving rise to a continuous rotation of the coil and the axle.

Question. State the principle of an electric generator.
Answer: An electric generator is based on the principle of electromagnetic induction. When a rectangular coil is rotated in a uniform magnetic field, an induced emf is generated between the ends of the coil.

Question sources produce alternating current?
Answer: A.C. generator and common inverter used in houses for emergency power supply produce alternating current.

Question. State and define S.I unit of magnetic field?
Answer: The S.I unit of magnetic field is Tesla (T). The magnetic field strength is said to be one Tesla if 1meter long conductor carrying 1 ampere current experiences 1 Newton force, when placed perpendicular to the direction of magnetic field.

Question. When is the force experienced by a current-carrying conductor placed in magnetic field largest?
Answer: The force experienced by a current carrying conductor placed in a magnetic field is largest when the conductor is placed with its length in a direction perpendicular to that of magnetic field.

Question. Why don’t two magnetic lines of force intersect each other?
Answer: No, two magnetic field lines can ever intersect each other. If they do, then it would mean that at the point of intersection there are two directions of magnetic field, which is not possible. 

Question. What is electric fuse? Where it is connected in a circuit?
Answer: An electric fuse is a safety device which is made up of a wire made of copper or aluminum or a tin lead alloy. An electric fuse must be connected in the path of the circuit so that overloading which can cause fire due to short circuit can be avoided.

Question. When does an electric short circuit occurs?
Answer: If either the insulation of wires used in an electric circuit is damaged or there is a fault in the appliances, live wire and neutral wire may come in direct contact. As a result, the current in the circuit abruptly rises and short circuiting occurs.

Question. Why is the earth pin thicker and longer than the live and the neutral pins?
Answer: it is thicker so that it does not enter into the live or neutral sockets. It is made longer so that it gets connected to the earth terminal earlier than the live and neutral pins. This ensures the safety of the user.

Question. A current-carrying straight conductor is placed in the east-west direction. What will be the direction of the force experienced by this conductor due to earth’s magnetic field? How will this force get affected on? (a) reversing the direction of floe of floe of current (b) doubling the magnitude of current.
Answer: The direction of earth’s magnetic field is from U-south to 0-north. Let current is from west to east. Therefore, force is vertically upwards.
(a) By reversing the direction of current, the direction of will be reversed i.e. vertically downwards.
(b) The magnitude of the force is doubled.

Question. Give two uses of electromagnets.
Answer: (i) It is used in cranes for lifting heavy loads.
(ii) used in electric bells.

Question. Name two safety measures commonly used in electric circuits and appliances.
Answer: Two safety measures are:
(a) use of earth wire and proper earthing.
(b) use of fuse.

Question. Name some devices in which electric motors are used.
Answer: Electric motors are used in all devices where we want to convert electrical energy into Mechanical energy. In our houses, electric motors, coolers, mixer grinders, washing machines, computers etc motor is used.
(a) use of earth wire and proper earthing.
(b) use of fuse.

Question. What type of core is used to make an electromagnet?
Answer: Soft iron core is used in making an electromagnet.

Question. State the observation made by Oersted on the basis of his experiment with current carrying conductors.
Answer: A magnetic field is produced near a current carrying conductor which last so long till there is current in the conductor on reversing the current the direction of magnetic field is also reversed.

Question. What does the thumb indicated in Fleming’s right hand rule?
Answer: Thumb indicate the direction of force on conductor i.e. motion of the conductor.

Question. State the direction of the magnetic field inside the bar magnet.
Answer: In a magnet, magnetic field lines goes from S pole to N pole.

Question. What is short-circuiting in an electric supply?
Answer: When a neutral wire and live wire come in contact with each other short circuit takes place.

Question. Why are magnetic field lines closed curves?
Answer: By convention the magnetic field lines are the path traced by north pole which emerges from north pole and goes to the south pole and inside the magnet the direction of field lines are from south pole to north pole, forming continuous closed path.

Question. Write any one method to induce current in a coil.
Answer: By moving a magnet towards the coil or vice versa, current can be induced in the coil.

Question. State two ways by which the strength of an electromagnet can be increased.
Answer: By increasing the strength of current and number of turns of the solenoid we can increase the strength of an electromagnet.

Question. An alternating electric current has a frequency of 50 Hz. How many times does it change its direction in one second? Give reason for your answer.
Answer: 100 times in one second because one complete cycle involves two times change of direction.

Question. (a) Name the type of electric current generated by the most of the power stations in our country.
(b) Why is it preferred over the other type?
(c) State the frequency of the power supply generated in India.
Answer:
(a) Alternating current
(b) AC can be transmitted at high voltage using step up transformer to prevent loss in transmission.
(c) 50 Hz

Question. How is the magnetic field produced in a solenoid used?
Answer: Magnetic field produced in a solenoid can be used in making a soft iron piece electromagnet.

Question. Mention the special feature regarding shape of magnetic field lines.
Answer: Magnetic field lines are continuous closed loops.

Question. (a) In a pattern of magnetic field fines due to a bar magnet, how can the regions of relative strength be identified?
(b) Compare the strength of field near the poles and middle of a bar magnet.
Answer:Ans : 
(a) More the density of the magnetic field lines i.e. more closer the magnetic field lines more the strength of magnetic field.
(b) Near the poles magnetic field lines are closer than the middle of a bar magnet. So magnetic strength is more near poles than middle part of bar magnet.

Question. State the direction of magnetic field in the following case:

Answer: Perpendicular to both current and force on the conductor outward the plane of paper.

Question. Mention the angle between a current carrying conductor and magnetic field for which the force experienced by this current carrying conductor placed in magnetic field is largest?
Answer: If the angle between a current carrying conductor and magnetic field is 90° then the force experienced by the conductor is maximum.

Question. Suggest one way of discriminating a wire carrying current from a wire carrying no current.
Answer: When a magnetic compass is brought near a current carrying conductor it will be deflected. If magnetic compass remains undeflected near a conductor then there is no current in it.

Question. Identify the type of magnetic fields represented by the magnetic field fines given below and name the type conductors which can produce them.

Answer: 

a. Magnetic field lines of a current carrying circular loop.
b. Magnetic field lines in a solenoid.

Question. What does the direction of thumb indicate in the right-hand thumb rule?
Answer: Thumb points the direction of current in the conductor holding a straight conductor in right hand.

Short Answer Type Questions :

Question. (a) Draw magnetic field lines of a current carrying circular loop. Identify the region where field is strongest and why?
(b) List two properties of magnetic field lines. 
Answer:(a) On observing the field lines, it shows that magnetic field due to the current carrying circular loop is maximum and normal to the current carrying loop at its center because magnetic field due to each part of loop adds up.
(b) (i) No two magnetic field lines intersect with each other at any point.
(ii) More crowded field lines means a stronger magnetic field.

Question. Why and when does a current carrying conductor kept in magnetic field experiences force? List the factors on which direction of force will depend. 
Answer:The movement of electrons takes place in the conductor in a particular direction when current is passed through it. These charged particles are moving in the magnetic field which experiences force.The current carrying conductor has its own magnetic field, when it superimpose the magnetic field of magnet. Due to this, current carrying conducter experiences a force. Thus conductor experiences a force when placed in a uniform magnetic field.
Factors on which direction of force depends:
(i) The direction of force depends upon the direction of magnetic field.
(ii) It also depends upon the direction of current flowing through the conductor.

Question. How is the strength of magnetic field near a straight current-carrying conductor
(i) related to the strength of current in the conductor?
(ii) is affected when the direction of flow of current is reversed?
Answer:(i) The strength of magnetic field is directly proportional to the strength of current.
(ii) If we reverse the direction of current, the direction of magnetic field will also be reversed.

Question. State two ways by which the strength of an electromagnet is increased. 
Answer:(i) Increase in number of turns in the solenoid.
(ii) Increase in the strength of current flowing in the solenoid.

Question. An alpha particle (positively charged) enters a magnetic field at right angle to it as shown in figure. Explain with the help of relevant rule,the direction of force acting on the alpha particle. 

Answer:The force will act in upward direction given by thumb, if forefinger points in the direction of magnetic field and the middle finger points in the direction of current, according to Fleming’s left hand rule.

Question. (i) A compass needle gets deflected when brought near a current carrying conductor. Why?
(ii) What happens to the deflection of needle when current in the conductor is increased? 
Answer:(i) It is because current carrying conductor produces a magnetic field which superimposes with magnetic field of compass needle due to which needle of compass gets deflected.
(ii) The deflection in the magnetic needle will increase as the strength of current increases.

Question. Identify the type of magnetic field represented by the magnetic field lines given below and name the type of conductors which can produce them.

Answer:(a) These magnetic field lines are produced by a current carrying loop.
(b) These are magnetic field lines produced by solenoid.

Question. Define a solenoid. Compare the magnetic field produced by a solenoid with that of a bar magnet. 
Answer:A coil of many circular turns of copper wire wrapped in the shape of a cylinder, is called a solenoid.The magnetic field lines in a solenoid, through which current is passed, is very similar to that of a bar magnet. One end of the coil acts like the magnetic north pole, while the other acts like the magnetic south pole. The magnetic field produced by a long solenoid has all the properties of the field produced by a bar magnet.

Question. Distinguish between a bar magnet and an electromagnet.
Answer:

Question. Can a freely suspended current carrying solenoid stay in any direction? Justify your Answer: What will happen when the direction of current in the solenoid is reversed? Explain. 
Answer:A current carrying solenoid behaves like a bar magnet. When it is suspended freely it will stay in north–south direction. On reversing the direction current, it will turn to 180°° because its polarity will be reversed.

Question. A uniform magnetic field is directed vertically upwards. In which direction in this field forces an particle (+ve charged) be projected to that it is deflected southward? Name and state the rule you have to use to find the direction in this force. 
Answer:The direction of motion of particles is from west to east. Fleming’s left hand rule is used to find the direction of force.

Question. For the circular coil carrying current shown below draw magnetic field lines. Decide which of its face behaves as north pole and which face behaves as south pole. Give reason to justify your answer
Answer:Front face behaves like a north pole as field emerges out of it. Rear face behaves as south pole as field enters into this face.

Question. You are given three identical looking bars one of which is a magnet, the other made of a magnetic material and the third made of a non magnetic material. Using just these three bars how will you find out which is which? 
Answer:Bring one bar close to the other two one by one: if the bar attracts one of these and does not attract the
other one, the bar which is not attracted is made of non-magnetic material and the bar in our hand is
a magnet or a bar of magnetic material. Keep one bar on the table and move other bar along its length
from one end to the other, if uniform attraction is felt the bar in our hand is a magnet and vice versa.

Question. Describe an activity to show magnetic field lines are produced when current is passed through circular coil.

Answer:(i) Take a rectangular cardboard having two holes.
(ii) Insert a circular coil through these holes, normal to the plane of paper.
(iii) Connect the ends of coil in series with a battery, and key.
(iv) Sprinkle iron filings uniformly on the cardboard.
(v) Plug the key.
(vi) Tap the cardboard gently a few times. Note the pattern of the iron filings.
(vii) The pattern of magnetic field lines will be same as the pattern of iron filings.

Question. What is meant of solenoid? How does a current carrying solenoid behave? Give its main use.
Answer:The long coil containing large number of close turns of insulated copper wires wrapped around, is called a solenoid.
Current carrying solenoid behaves like a bar magnet. It is called an electromagnet.
It is used for making electromagnets.

Question. With the help of diagram of experimental set up describe an activity to show that the force acting on a current carrying conductor placed on magnetic field increases with increase in field strength.
Answer:(i) Take an aluminium rod, AB of size 3 inches.
(ii) Suspend it horizontally using connecting wires
(iii) Place a horse-shoe magnet in such a way that the rod lies between the two poles with magnetic field directed upwards.
(iv) Put north pole of the magnet vertically below and south pole vertically above the rod.
(v) Connect aluminium rod in series with the battery and key.
(vi) Now pass the current in the rod from B to A.
(vii) Aluminium rod will be displaced towards the left.
(viii) Now bring a stronger horse-shoe magnet and observe the displacement of rod.
(ix) The displacement of rod will increase with the increase in strength of the magnetic field.

Question. Write one application for each of the following:
(a) Right-hand Thumb Rule,
(b) Fleming’s left Hand Rule,
(c) Fleming’s Right Hand Rule.
Answer:(a) It is used to find the direction of magnetic field in a coil of wire and electric current in a straight conductor.
(b) It is used to find the direction of force exerted on a current carrying conductor in a magnetic field.
(c) It is used to find the direction of induced current in a closed circuit placed in a changing magnetic field, e.g. in an electric generator.

Question. How will the magnetic field produced at a point due to a current carrying circular coil change if we:
(i) increase the current flowing through the coil, (ii) reverse direction of current through coil,
(iii) increase the number of turns in the coil? 
Answer:(i) The strength of magnetic field will increase. ( B ∝ I)
(ii) The direction of magnetic field will be reversed.
(iii) The magnetic field produced will increase because magnetic field produced is directly proportional to the number of turns in the coil.

Question. (a) Mention the factors on which the direction of force experienced by a current carrying conductor placed in a magnetic field will depend.
(b) Under what conditions is the force experienced by a current carrying conductor placed in a magnetic field maximum?
(c) A proton beam is moving along the direction of a magnetic field. What force is acting on proton beam? 
Answer:(a) (i) direction of current, (ii) direction of magnetic field.
(b) When direction of current is perpendicular to the direction of magnetic field, the force experienced will be maximum.
(c) No, force is exerted by a proton beam because proton beam is moving along the direction of magnetic field.

Question. List three sources of magnetic field.
Answer:(i) Magnetic field is associated with bar magnet
(ii) A current carrying conductor produces magnetic field.
(iii) A current carrying curricular loop also produces magnetic field.

Question. An alpha particle (+ve charged particle) enters a magnetic field at right angle to it as shown in figure.
Explain with the help of a relevant rule, the direction of force acting on the alpha particle.

Answer: Force on a-particle will be in the upward direction as per Fleming’s left hand rule.

Question. (a) Name four appliances wherein an electric motor is used as an important component. In what respect it is different from generator?
(b) Define the terms used in the generator
(i) armature
(ii) slip rings
(iii) brushes
Answer: (a) The four appliances which have electric motor inside them are
(i) Mixers (ii) Washing machine (iii)Refrigerators (iv) Blenders
(b) (i) Armature – Armature is a coil of large number of turns of insulated copper wire wound over a soft iron core.
(ii) Slip rings- Slip Rings one two rings made up of brass which rotates along with the coil.
(iii) Brushes- Brushes are made up of carbon which are pressed against the slip rings and are connected to external circuit where output is obtained.

Question. Why does a compass needle get deflected when brought near a bar magnet?
Answer: The compass needle is small bar magnet. When a compass needle is brought near a bar magnet then due to repulsive force between unlike poles and attraction between unlike poles, the compass needle is deflected and settle in the direction of net magnetic field.

Question. (a) What is short circuiting?
(b) What is overloading? How can you avoid overloading?
Answer: (a) Short circuiting means when live wire and the neutral wires come in contact with each other. Due to this resistance of the circuit becomes very small and huge amount of
current flows through the circuit which is turn produces more heat which can cause fire.
(b) Overloading means large amount of current flows in the circuit. It can happen when many electrical appliances of high power ratings are connected in a single socket. It can be
avoided by the following methods:
(i)Not use too many appliance is a single socket
(ii)To apply preventive methods of short circuiting.

Question. Define electromagnetic induction? Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Explain.
Answer: Electromagnetic induction means the production of induced current in a closed coil due to the change in the magnetic field. When current in coil A is changed, magnetic flux sets up around coil A due to which some magnetic field set up in the coil B thus some induced current flow through coil B due to which galvanometer deflects.

Question. Why does a current carrying conductor kept in a magnetic field experience force?
What is the direction of force acting on the conductor?
Answer: A current carrying coil contains charged particles which experiences a force (Bqv). The total force experienced by the charged particle is equal to the force experienced by the conductor which is perpendicular to both the magnetic field and the direction of current in the conductor.

Question. What is the function of an earth wire? Why is if necessary to earth metallic casing of electric appliance?
Answer: Earth will acts as a safety device. When live wire touches the metallic appliance then electric current flows through castling to the earth instead of human body and thus we
prevent ourselves from getting shock. It is necessary to earth metallic casing of the appliance because it saved electrical appliance from burning and prevent us from electric shock.

Question. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer: The earth wires functions as a safety measure, especially for those appliances that have a metallic body, like heater, electric, press, room cooler etc. The metallic body of the
appliance is connected to the earth wire, which provides a low resistance conducting path for electric current. It ensures that any leakage of current to the metallic body of an appliance keeps it potential same as of earth. As a result, the user would not get severe electric shock, even if he touches the body of appliance.

Question. A coil of insulated copper wire is connected to a galvanometer. What would happen if a bar magnet Is.
(i) Pushed into the coil?
(ii) Withdrawn from Side the coil?
(iii) Held stationary inside the coil?
Answer: (i) Due to change in magnetic flux linked with coil, the galvanometer shows deflection (say towards right).
(ii) Due to change in magnetic flux linked with coil, the galvanometer shows deflection (say towards left opposite to that in case one).
(iii) As it is stationary no change in magnetic flux linked with coil, so galvanometer shows no deflection.

Question. In activity 13.7, how do we think the displacement of rod AB will be affected if
(i) current is rod AB is increased,
(ii) a stronger horse shoe magnet is used, and
(iii) length of the rod AB is increased?
Answer: (i) O increasing the current in rod AB its displacement will increase.
(ii) If stronger horse-shoe magnet is used then the displacement of rod AB will increase.
(iii) If length of the rod is increased, force acting on it will increase and hence, displacement of the rod increases.

Question. State Fleming’s left-hand rule.
Answer: Fleming’s left hand rule states that stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other. If the forefinger shows the direction of the magnetic field and central finger that of the current, then the thumb will point towards the direction of motion of the conductor.

Question. State the rule to determine the direction of a (i) magnetic field produced around a straight current carrying conductor
(ii) force experienced by a current carrying straight conductor
(iii) current induced in a coil due to its rotation in a magnetic field.
Answer: (i) To know the direction of magnetic field produced around a straight conductor we
make use “Right hand thumb Rule”.
(ii) To find the direction of force experienced by a current carrying straight conductor placed in a magnetic field we make use “Fleming’s left hand rule”.
(iii) For finding the direction of current induced in a coil we use “Fleming’s right hand rule”.

Question. State three factor on which magnetic field produced by a current carrying solenoid depends.
Answer: (1) The strength of the current flowing through the solenoid.
(2) No. of turns of the wire of the solenoid.
(3) Nature of the material inside solenoid.

Question. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is
(i) pushed into the coil.
(ii) withdrawn from inside the coil
(iii) held stationary inside the coil?
Answer: (i)When a bar magnet is pushed into the coil of insulated copper wire connected to a galvanometer, galvanometer gives a deflection towards left.
(ii) When the bar magnet is withdrawn from inside the coil, again an induced current is set in coil that deflect the galvanometer towards right.
(iii) If the bar magnet is held stationary inside the coil, then no induced current is set and galvanometer does not show any deflection.

Question. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220V) that has a current rating of 5.A. What result do you expect? Explain.
Answer: Power rating of electric oven (P) = 2 kW = 2000 W
Current drawn (I) = P/V = 2000/220 = 9.09 A.
As the current rating of domestic electric circuit is only 5A the oven draws a current of 9.09 A. Which is more than the current rating; hence the circuit will be damaged due to overheating/overloading.

Question. What precaution should be taken to avoid the overloading of domestic electric circuit?
Answer: We should take following precaution to avoid the overloading of domestic electric
circuit:
(a) Two separate circuits should be used, one of 5A current rating of bulbs, fans, tubes etc.
and the other 15 A current rating for appliances with higher current rating such as geysers, air coolers, electric iron, electric stoves etc.
(b) Too many appliances should never be connected to a single socket.
(c) A fuse of appropriate current rating should be used with the electric circuit.

Question. We know a current carrying conductor placed in a magnetic field experiences a force due to which the conductor moves. How do we think the rod displaces if-
(a) current in rod is increased
(b) a stronger horse shoe is inserted
(c) length of the rod is increased.
Answer:  Force acting on current carrying conductor
F=BIL
(a) When I increase, F also increases hence displacement of the rod increases.
(b) When a stronger horse shoe magnet is inserted, magnetic field B increases. So force F increase. Hence displacement increases.
(c) When I increase, force increases and hence displacement increases.

Question. (a) Distinguish between A.C and D.C?
(b) Which source produces alternating current?
Answer:

Question. How does a solenoid behave like a magnet? Can you determines the north and south poles of a current carrying solenoid with the help of a bar magnet? Explain.
Answer: When current is passed through a solenoid coil, magnetic field is produced due to presence of turns in same direction. As a result, the resultant magnetic field is very strong
and uniform.
Solenoid behaves like a strong bar magnet. We can determine the poles of magnet formed by solenoid. The end of solenoid connected with positive terminal behaves like South Pole and the end connected with negative terminal behaves as North Pole.

Question. Imagine that you are sitting in chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Answer: An electron beam moving horizontally from back wall towards the front wall is equivalent to a current flowing in the opposite direction. The deflection of electron beam as seen by the observer is to his right side. On applying Fleming’s left-hand rule we find that the magnetic field is acting in vertically downward direction.

Question. Suppose your science teacher asks you to demonstrate the phenomena of EMI with following materials:
(a)Two different coils land 2 of copper wire having large no. of turns 50 and 100 respectively.
(b) A non conducting cylinder.
(c) A battery
(d) A plug key
(e) A galvanometer
(i) Draw a labeled diagram of your demonstration setup.
(ii) How will you prove the phenomena of EMI.
Answer: (i)

(ii) When key is closed, there is deflection in galvanometer.

Question. List the properties of magnetic lines of force.
Answer: Properties of magnetic field lines of force as follows:
a. Outside a magnet, the field lines are directed from N-pole of magnet towards S-pole and inside the magnet lines are directed form S-pole to N-pole.
b. Magnetic field lines are closed curves.
c. No two magnetic field lines intersect each other.
d. Relative strength of magnetic field lines is given by degree of closeness of the filed lines.

Question. (a) What is the standard colour code followed for
(i) live
(ii) neutral and
(iii) earth wires used in electric circuits?
(b) Which part of an electric appliance is earthed and why?
Answer: (a) The standard colour code for
Live wire – Red
Neutral – Black
Earth – Green respectively.
(b) The metallic case of an electrical appliance is earthed because metals are good conductors of electricity and in case if current exceeds i.e. live wire touches the metallic case
of an appliance and then due to earthing all the excess amount of current flows down to the earth and we prevent ourselves from an electric shock.

Question. Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Answer: Yes, a current is induced in the coil B.
When the current in the coil A is changed, the magnetic field associated with it also changes.
As coil B is placed close to A, hence magnetic field lines around this coil also change. Due to change in magnetic field lines associated with coil B, an induced current is also induced in it.

Question. An electron enters a magnetic field at right angles to it as shown in fig. The direction of the force acting on the electron will be:
(a) to the right (b) to the left (c) out of the page (d) into the page
Answer: When a conductor carrying current is placed perpendicular to the direction of magnetic field, the acting on it is given by Fleming’s left hand rule. Since the direction of current is the same as that of the motion of a positive charge, the direction of force acting on it when moving perpendicular to the direction of magnetic field is the same as that acting on a current-carrying conductor placed perpendicular to the direction of magnetic field.
Obviously, the force acting on an electron is opposite to that. Therefore, in this case it is into the page.

Question. Consider a circular wire lying in the plane of the table and the direction current in it is antilock wise.
(i) Draw the magnetic field lines produced around it.
(ii) Why does magnetic field at the center of current carrying circular loop appear straight? Explain with diagram.
Answer: (i)

(ii) Because of large curvature of magnetic field lines at centre.

Question. List three methods of producing magnetic field.
Answer: Three methods of producing magnetic fields are as follows:
(a) Magnetic field can be produced by placing a permanent magnet or a horse-shoe magnet at the place, where magnetic field is required.
(b) Magnetic field is produced around a current carrying straight conductor or a current carrying coil.
(c) A very good method to produce magnetic field is due to flow of current in a solenoid.

Question. What is the principle of an electric motor?
Answer: An electric motor is based on the principle that the current carrying conductor experiences a force when placed in a magnetic field. If the direction of the magnetic field and
that of the current are mutually perpendicular, then the direction of the force is given by Fleming’s left-hand rule.

Question. What is the principle of electric motor? State the function of (i) split ring (ii) field magnet used in electric motor.
Answer: Electric motor works on the principle that a current carrying conductor placed perpendicular to a magnetic field experiences a force.
(i) Split ring – It reverses the dissection of current in the armature and thus direction of force is also reserved. As a result dc motor continues to rotate in same direction.
(ii) Field magnet – It provided strong magnetic field.

Question. A magnet is moving towards a coil as shown in figure.

(1) Which phenomenon is shown in figure.
(2) Which physical quantity is between magnet and coil? set up in the coil when there is a relative motion
(3) What may be the cause of production of that physical quantity?
Answer: (1) Electromagnetic induction
(2) Induced current
(3) Change in magnetic lines of forces through coil

Question. What is a solenoid? Draw magnetic field lines showing the magnetic field inside and outside the current carrying solenoid?

Answer: A solenoid is a coil of many turns of insulated copper wire closely wound in the shape of a ring.

Question. (a) Define the term current rating of an electric fuse?
(b) Name the material used to make electric fuse?
(c) Name two safety measure commonly used in electric circuit and appliances?
Answer: (a)The maximum amount of current that can be passed through the fuse wire without melting it.
(b) Copper or alloy of lead acid tin.
(c) Electric fuses and earth wire.

Question. Explain different ways to induce current in a coil.
Answer: Different ways to induce current in a coil are as follows:
(a) If a magnetic field is changed around a coil then an induced current is set up in the coil.
(b) If a coil is moved in magnetic field, then again an induced current is set up in the coil.
(c) If a coil is rotated in a uniform magnetic field

Question. If we place a compass needle near straight conductor carrying current (a)What happens to the deflection of the compass needle if the direction of current reversed. Is
(b)What change will you notice in the compass needle if it is moved away from conductor but the current through the conductor remains the same?
Answer: (a) Direction of deflection will reverse
(b) Deflection will decrease

Question. The magnetic field associated with a current-carrying straight conductor is in anticlockwise direction. If the conductor was held along the east-west direction, what will be the direction of current through it? Name and state the rule applied to determine the direction of current.
Answer:  Direction of current – east to west as determined by Right-hand thumb rule. Ri’-lu-Uand Thumb Rule: If we hold a current-carrying conductor by right hand in such a way that the stretched thumb is along the direction of current, then the curly fingers around the conductor represents the direction of field lines of magnetic field.

Question. Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Answer: Yes, when a current in coil A changes, magnetic field lines linked with coil B also change. Hence, due to change in number of magnetic field lines, there is an induced current in coil B. ,

Question. How is the strength of magnetic field near a straight current-conductor (i) related to the strength of current in the conductor?
(ii) is affected by changing the direction of flow of current in the conductor?
Answer:
(i) The strength of magnetic field around a straight current conductor increases on increasing the strength of current in the conductor or vice versa.
(ii)The direction of magnetic field around a straight current carrying conductor gets reversed if the direction of current through that conductor is reversed.

Question. Two coils A and B of insulated wires are kept close to each other. Coil A is connected to a galvanometer while coil B is connected to a battery through a key. What would happen if (i) a current is passed through coil B by plugging the key, and (ii) the current is stopped by removing the plug from the key?
Explain your answer mentioning the name of the phenomenon involved.
Answer: In both the given cases, galvanometer shows momentary deflection but in opposite direction. In coil A, magnetic field lines [increased in case (i) and decreased in case (ii)] induce a potential difference across the coil A which sets up induced electric current in coil A. It is shown by the deflection in galvanometer. This is known as electromagnetic induction.

Question. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220.V) that has a current rating of 5 A. What result do you expect? Explain.

Answer: Current drawn by electric oven
Current rating of the circuit = 5 A
So, fuse will blow off and power supply will cut off

Question. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Answer: When the length of current-carrying conductor and direction of magnetic field are perpendicular to each other, the maximum force is experienced by the current-carrying conductor.

Question. State one main difference between A.C and D.C. Why A.C is preferred over D.C for long range transmission of electric power? Name one source each of D.C and A.C.
Answer: Difference between A.C. and D.C. The alternating current (A.C.) reverses its direction periodically whereas the direct current (D.C.) always flows in one direction.
A.C. is preferred over D.C. because it can be transmitted over long distance without much loss of energy.
D.C. source : Battery A.C. source : A.C. generator

Question. State the consequences that can lead to a short circuit. Or
One of the major cause of fire in office building is short circuiting. List three factors which may lead to the short circuit.
Answer: It occurs as a consequence of failure of electrical insulation’s due to which live wire comes in direct contact with neutral or earth wire.
presence of external conducting material such as water which is introduced accidentally into the circuit.
electrical appliances are forced to operate when its moving parts are jammed.
connection of current carrying parts of electrical equipment’s comes in contact to one another due to human or natural cause and use of less rating wires.
When this happens, there is an excessive electric current which can damage the circuit and may also cause electrical fires.

Question. (a) Two magnets are lying side by side as show.
Draw magnetic field line between poles P and Q.
(b) What does the degree of closeness of magnetic field lines near the poles signify?
Answer:

(b) The degree of closeness of magnetic field lines near the poles signify that the field is stronger there, i.e. the pole of another magnet when placed in the magnetic field experiences a greater force where the field lines are crowded.

Question. A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its north pole towards one face of the coil is
(i) moved quickly towards it,
(ii) moved quickly away from the coil and
(iii) placed near its one face?
Name the phenomenon involved.
Answer:
(i) Deflection in the galvanometer needle will be more on right-side.
(ii) Larger deflection in opposite direction as compared to the case (i) will be seen. (Hi) No deflection.
The phenomenon involved is electromagnetic induction.

Question. What is meant by solenoid? How does a current carrying solenoid behave? Give its main use.
Answer:  Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard etc.) such that its length is greater than its diameter is called solenoid. img
When current is flowing through the solenoid, the magnetic field line pattern resembles exactly with those of a bar magnet with the fixed polarity, i.e. North and South pole at its ends and it acquires the directive and attractive properties similar to bar magnet. Hence, the current carrying solenoid behave as a bar magnet.
Use of current carrying solenoid: It is used to form a temporary magnet called electromagnet as well as permanent magnet.

Question. For the current carrying solenoid as shown below, draw magnetic field lines and giving reason explain that out of the three points A, B and C at which point the field strength is maximum and at which point it is minimum.

Answer: Outside the solenoid magnetic field is minimum. At the ends of solenoid, magnetic field strength is half to that inside it. So Minimum – at point B; Maximum – at point A

Question. What is short circuiting? State one factor/condition that can lead to it. Name a device in the household that acts as a safety measure for it. State the principle of its working.
Answer: Short circuiting: When electric circuit offers very low resistance to the flow of current through it, the current increases heavily and the circuit is said to be short circuited. It occurs when live wire touches the neutral wire. This happens due to the damage in insulation of the power lines.
Safety measure device: Fuse.
Working principle of fuse: It works on the heating effect of electric current or Joule’s law of heating.
According to this law, the heat produced in a resistor is directly proportional to the (i) square of current for a given resistance.
(ii) resistance for a given current and (iii) time for which the current flows through the resistor.
H = I2Rt
So, when current in the circuit increases, the wire with low melting point in it melts to the heat generated.
Hence, the circuit breaks and electrical devices and appliances are saved.

Question. Write one application of each of the following:
(a) Right-hand thumb rule (b) Fleming’s left hand rule
(c) Fleming’s right hand rule
Answer:
(a) Right-hand thumb rule is used to find the direction of magnetic field in a coil of wire and the electric current in a straight conductor.
(b) Fleming’s left hand rule is used to find the direction of force exerted on a current-carrying conductor placed in a magnetic field as in electric motor.
(c) Fleming’s right hand rule is used to find the direction of induced current in a closed circuit placed in changing magnetic field as in electric generator.
Q. State one main difference between A.C. and D.C. Why is A.C. preferred over D.C. for long range transmission of electric power? Name one source each of D.C. and A.C.
Answer. Difference between A.C. and D.C.: The alternating current (A.C.) reverses its direction periodically whereas the direct current (D.C.) always flows in one direction.
A.C. is preferred over D.C. because it can be transmitted over long distance without much loss of energy.
D.C. source: Battery A.C. source: A.C. generator

Question. With the help of a diagram of experimental setup describe an activity to show that the force acting on a current carrying conductor placed in a magnetic field increases with increase in field strength.
Answer:
Aim : To show that force acting on a current carrying conductor placed in a magnetic field increases with the field strength.
Apparatus Required : Aluminium rod, stand horse shoe magnet of different intensity, cell, key and connecting wires.
Procedure :
1. .Arrange the set-up as shown in figure.

2.Plug the key, the current flowing through the rod from Q to P observe the displacement of rod.
3.Now unplug the key and remove the first horse shoe magnet and place the second horse shoe magnet of higher magnetic field strength in a similar manner to that of first.
4.Plug the key, the current again flow through the rod from Q to P. Again observe the deflection of rod.
5.Now bring both’the magnet closer together (to ensure greater magnetic field than that of previous case). Again observe the motion of rod.
Observations : Each time, the conductor moves faster than that of previous one. It is possible only when conductor gets accelerated more each time which required more force. (F = ma) Thus, if the magnetic field strength is increased, the rod will experience a greater force and move faster.
Conclusion : The force acting on a current carrying conductor placed in a magnetic field increases with increase in field strength.

Question. State one main difference between A.C. and D.C. Why is A.C. preferred over D.C. for long range transmission of electric power? Name one source each of D.C. and A.C.
Answer: Difference between A.C. and D.C.: The alternating current (A.C.) reverses its direction
periodically whereas the direct current (D.C.) always flows in one direction.
A.C. is preferred over D.C. because it can be transmitted over long distance without much loss of energy.
D.C. source: Battery A.C. source: A.C. generator

Question.What are magnetic field lines? Justify the following statements
(a) Two magnetic field lines never intersect each other.
(b) Magnetic field lines are closed curves.
Answer:
Magnetic field lines: It is defined as the path along which the unit North pole (imaginary) tends to move in a magnetic field if free to do so.
(a) The magnetic lines of force do not intersect (or cross) one another. If they do so then at the point of intersection, two tangents can be drawn at that point which indicates that there will be two different directions of the same magnetic which field, i.e. the compass needle points in two different directions which is not possible.
(b) Magnetic field lines are closed continuous curves. They diverge from the north pole of a bar magnet and converge its south pole. Inside the magnet they move from south pole to north pole.

Question. Write one application of each of the following:
(a) Right-hand thumb rule (b) Fleming’s left hand rule
(c) Fleming’s right hand rule
Answer:
(a) Right-hand thumb rule is used to find the direction of magnetic field in a coil of wire and the electric current in a straight conductor.
(b) Fleming’s left hand rule is used to find the direction of force exerted on a current-carrying conductor placed in a magnetic field as in electric motor.
(c) Fleming’s right hand rule is used to find the direction of induced current in a closed circuit placed in changing magnetic field as in electric generator.

Question. (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an electric motor.
(i) Armature, (ii) Brushes, (iii) Split ring
Answer:
(a) Fleming’s left hand rule: If we stretch thumb, forefinger and middle finger of left hand perpendicular to each other in such a way that forefinger points in the direction of magnetic field, middle finger points in the direction of current then the thumb will point in the direction of motion/force on the current carrying conductor.
(b) Principle of working of electric motor: A current carrying coil placed in a magnetic field experience a torque. If the coil is free to move it will rotate in the magnetic field.
(c) (i) Armature: The soft iron core on which the coil is wound along with coils is called armature which enhances the power of motor.
(ii) Brushes: Brushes help in transfer of current between coil and external circuit.
(iii) Split rings reverses the direction of current after every half rotation of the coil so that the direction of torque/force on the coil remains and it continuous to rotate.

Question. Draw the pattern of lines of force due to a magnetic field through and around a current carrying loop of wire. How would the strength of the magnetic field produced at the centre of the circular loop be affected if
a. the strength of the current passing through this loop is double?
b. the radius of the loop is reduced to half of the original radius?
Answer: The pattern of lines of force due to a magnetic field through and around a current carrying loop of wire is shown below

a. Strength of magnetic field is doubled when the current through the loop is doubled B α I .
b. Strength of magnetic field is doubled when the radius of the loop is halved B α 1/F

Question. Name any three factors on which the magnitude of the magnetic field due to solenoid depends.
Answer: Factors on which the magnitude of the magnetic field due to solenoids
a. number of turns in the solenoid
b. area of cross section of the coil
c. strength of current in solenoid

Question. Draw the pattern of field lines due to a solenoid carrying electric current. Mark the north and south poles in the diagram.
Answer: The pattern of the magnetic field lines is as shown in figure.

Question. Define magnetic field. Describe an activity to draw magnetic field lines around a bar magnet from one pole to another pole.
Answer: Magnetic field is the space around a magnet or a current carrying conductor in which its magnetic force can be experience.
Fix a plane white drawing sheet on a drawing board. Now take a bar magnet and a compass. Place the magnet at the middle of the paper and mark its boundary with the help of a pencil. Now place the compass near its N pole of the magnet and marks the positions of needle of the compass. Now move the compass on the drawing board. Coinciding south pole
of the compass with the previous marked point of N pole of the needle and so on, move forward from one end (N pole) to the another end (S pole) of the bar magnet.
Join all the marked points. You will get magnetic lines of force.

Question. Find the minimum rating of fuse that can be safely used on a line on which two 1.1 kW, electric geysers are to run simultaneously. The supply voltage is 220 V.
Answer: I = Total Power/V = nP /V
= 2 X 1.1kW/220V
= 2 X 1.1 X 1000 /220V W = 10 A
So a fuse wire of rating must be greater than 10 A.

Question. Can a freely suspended current carrying solenoid stay in any direction? Justify your answer. What will happen when the direction of current in the solenoid is reversed? Explain.
Answer: No, current carrying solenoid behaves like a bar magnet and will stay only geographical N and S direction. If the direction of current is reversed then the polarity of the magnet will change and hence will rotate through an angle of 180°.

Question. What is meant by electromagnetic induction? State the rule which helps in determining direction of induced current.
Answer: Electromagnetic induction is the phenomenon of production of emf (potential difference) or current in a coil due to change in magnetic field around it.
Fleming right hand rule: If we stretch our right hand thumb, forefinger and middle finger perpendicular to each other in such a way that forefinger points the direction of magnetic field, and thumb points the direction of force acting on the conductor (motion of the conductor), then the middle finger points the direction of induced current in the conductor.

Question. Horizontal component of earth’s magnetic field at a place is uniform and its direction is south to north. A high current through a horizontal power line flows at this place from west to east. Consider two points A and B at equal distances from the wire, respectively above and below it. Giving reason explain where is the field more at A or at B.
Answer: The direction of magnetic field due to current at A is from north to south and at B from south to north.
Therefore, at A earth’s magnetic field and field due to current are in opposite direction and at B earth’s magnetic field and magnetic field due to current are in same direction.

Question. A coil made of insulated copper wire is connected to a galvanometer. What will happen to the deflection of the galvanometer if this coil is moved towards a stationary bar magnet and then moved away from it?
Give reason for your answer and name the phenomenon involved.
Answer: In both the case there is a change in magnetic field associated with the coil, an induced current is produced in the coil, but in opposite direction. This phenomenon is called electromagnetic induction (EMI).

Question. What is meant by overloading of an electrical circuit?
Explain two possible causes due to which overloading may occur in household circuit. Explain one precaution that should be taken to avoid the overloading of domestic electric circuit.
Answer: Connecting large number of electric appliances in one socket whose load is more than the maximum permitted limit. The two possible cause are
a. all of a sudden supply of high voltage and
b. too many devices connected in a single socket.
Precautions:
a. use of voltage regulator,
b. load of a socket must be greater than its permitted rating.

Question. A coil of insulated wire is connected to a galvanometer.
Explain what happens if a bar magnet with its north pole towards one face of the coil is:
a. moved quickly towards the coil,
b. kept stationary inside the coil, and
c. moved quick away from the coil?
Answer: When a bar magnet is moved towards the coil there is change in magnetic field in
a. coil so a current is induced in the coil so galvanometer gives a deflection.
b. when magnet is kept stationary in the coil then due to no change in the magnetic field no current is induced in the coil.
c. when magnet is moved quickly away from the coil again there is change in magnetic field associated with the coil so again a current is induced but in the opposite direction.

Question. How will the magnetic field produced in a current carrying circular coil changes, if we increase the:
a. value of current flowing through it?
b. distance of point P from the coil?
c. number of turns of the coil?
Answer:
a. Magnetic field is directly proportional to current so magnetic field increases when current increases.
b. If we increase the distance of point P, magnetic field decreases.

c. On increasing the number of turns magnetic field increasing.

Question. What happens to the deflection of the compass needle placed at a point near current carrying straight conductor:
a. if the current is increased?
b. if the direction of current in the conductor is changed (reversed)?
c. if compass is moved away from the conductor?
Answer:
a. If the current increases deflection of compass increases.
b. If the direction of current is reversed the deflection in the compass needle is also reversed.
c. Deflection of the compass needle decreases when compass is moved away from the conductor.

Question. Differentiate overloading and short- circuiting.
Answer: Overloading means to draw current more than the permitted maximum current in the circuit which may be due to connecting many appliances in one socket.
In short circuiting, when live wire and neutral wire come in contact with each other then resistance of the circuit becomes minimum consequently the current in the circuit increases abruptly. It may be due to damage of insulation of wire.

Question. Write one difference between direct current and alternating current. Which one of the two is mostly produced at power stations in our country? Name one device which provides alternating current. State one important advantage of using alternating current.
Answer: Direct current has constant magnitude and unidirectional current. Alternating current changes its magnitude and direction alternatively.
a. Alternating current is produced in power stations in India.
b. AG generators are used to produce AC.
c. AC voltage can be increased or decrease with the help of a transformers.

Question. State the condition for electromagnetic induction to take place. A cylindrical bar magnet is kept along the axis of a circular coil as shown in the figure. Will there be a current induced in the coil if the magnet is rotated about its axis? Discuss.

Answer: Electromagnetic induction
a. Either coil or magnet or both must have a relative motion between them.
b. If there is a change in current in a coil then current will be induced in the another neighbouring coil.
No current is induced because there is no change in magnetic field.

Question. Draw a diagram to show how a magnetic needle deflects when it is placed above or below a straight conductor carrying current depending on the direction of the current in the conductor.
Answer: 

Question. For the circular coil carrying current shown alongside, draw magnetic field lines. Decide which of its face behaves as North Pole and which face as South Pole.
Give reason to justify your answer.

Answer: From the front face magnetic field emerges out of the coil and enters out from the back face so front face will behave as north pole and back face as south pole.

Question. A student performs an experiment to study the magnetic effect of current around a current carrying straight conductor with the help of a magnetic compass. He reports that:
a. the degree of deflection of the magnetic compass increases when the compass is moved away from the conductor.
b. the degree of deflection of the magnetic compass increases when the current through the conductor is increased.
Which of the above observations of the student appears to be wrong and why?
Answer: The first statement is wrong because the strength of magnetic field decreases when we move away from a current carrying conductor. So deflection in the compass, instead of increasing must decrease.

Question. A student while studying the force experienced by a current carrying conductor in a magnetic field records the following observations:
a. The force experienced by the conductor increases as the current is increased.
b. The force experienced by the conductor decreases as the strength of the magnetic field is increased.
Which of the two observations is correct and why?
Answer: First observation is correct because when current increases force also increase. From equation of force on a current carrying conductor F = BIl.F α I i.e. more current more force on a current carrying conductor in a magnetic field.

Question. (a) Electric fuse is an important component of all domestic circuits. Why?
(b) An electric oven of rating 2 kW, 220 V is operated in a domestic circuit with a current rating of 5 A. What result would you expect? Explain.
Answer: Electric fuse is a safety device which has high resistance and low melting point and prevents electric appliances during short circuiting and overloading. By melting itself, a fuse break the circuit.

Question. Why does a current carrying conductor kept in a magnetic field experience force? On what factors does the direction of this force depend? Name and state the rule used for determination of direction of this force.
Answer: Around a current carrying conductor a magnetic field is produced. When it is placed in a magnetic field then both fields interact each other, and current carrying conductor experience a force.
Fleming’s left hand rule: If we stretch right hand thumb, forefinger and middle finger perpendicular to each other in such a way that forefinger points the direction of magnetic field, middle finger points the direction of current, then thumb will point the direction of force on the conductor.

Question. What does the direction of thumb indicate in the right hand thumb rule? In what way this rule is different from Fleming’s left hand rule?
Answer: Thumb indicate the direction of current in a straight conductor held in right hand. Fleming’s left hand rule gives the direction of force on a current carrying conductor placed in magnetic field.
Fleming’s left hand rule : If we stretch right hand thumb, forefinger and middle finger perpendicular to each other in such a way that forefinger points the direction of magnetic field, middle finger points the direction of current, then thumb will point the direction of force on the conductor.

Question. A uniform magnetic field is directed vertically upwards. In which direction in this field should an a-particle (which are positively charged particles) be projected so that it is deflected south ward? Name and state the rule you have used to find the direction in this case.
Answer: Forefinger – direction of magnetic field (upwards).
Thumb – direction of force (southwards) Middle finger gives direction of current or direction of positively charged particle (East) i.e. from west to east a particles must be projected.

Question. (a) Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another.
(b) List any two properties of magnetic field lines.
Answer:
(a) Fix a plane white drawing sheet on a drawing board. Now take a bar magnet and a compass.
Place the magnet at the middle of the paper and mark its boundary with the help of pencil. Now place compass near N-pole of bar magnet and the position of needle of the compass. Now move the compass on the drawing board coinciding S-pole of the compass with the previous marked point of N of the needle and so on move forward from one end (N-pole) to the S-pole of the bar magnet. Join all the marked points. You will get magnetic lines of force.

(b) Properties of magnetic field lines.
(i) Magnetic field lines do not intersect each other.
(ii) Magnetic field lines emerge out at N-pole and goes to the S-pole whereas in magnet these travel from S-pole to N-pole.

Question. Under what condition does a current carrying conductor kept in a magnetic field experience maximum force? On what other factors does the magnitude of this force depend? Name and state the rule used for determination of direction of this force.
Answer: Force on a current carrying conductor in a magnetic field depends upon
a. length of the conductor
b. strength of the magnetic field
c. strength of the current
d. angle between direction of magnetic field and current.
Fleming’s Left Hand Rule:
Fleming’s left hand rule gives the direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it. According to Fleming’s left hand rule if we stretch our left hand thumb, forefinger and middle finger in such a way that forefinger points the direction of magnetic field, middle finger points the direction of current then thumb will give the direction of force on the conductor.

Long Answer Type Questions :

Question. Explain the underlying principle and working of an electric generator by drawing a labeled diagram. What is the function of brushes?
Answer: Electric generator labelled diagram is as follows:
Principle: An electric generator works on the principle of electromagnetic induction.
Working: Let the in the beginnings brushes B1 and B2 are kept pressed separately on rings R1 and R2 respectively. Let the axle attached to the rings is rotated such that arm AB of the
coil moves up and arm CD moves down in the magnetic field. Due to rotation of arms AB and
CD induced current are set up in them. As per Fleming’s right hand rule, induced current in
these arms along the directions AB and CD respectively and current flows into B1 and B2. After half rotation, arm AB moves downward and arms CD upward to change the direction
opposite to first case. Thus, after every half rotation current changes its direction and an alternate current is obtained in the generator.
Brushes are kept pressed on the two slip rings separately. Outer ends of the brushes are connected to the galvanometer. Thus, brushes help in transferring current from the coil
ABCD to external circuit.

Question. Current- time graph from two different sources are shown in the figure.

(i) Name the type of current shown by graph (A) and (B)?
(ii) Name any one source of shown by (A) and (B)?
(iii) What is frequency of current in case (B)?
(iv) Write two difference between current shown by (A) and (B)?
Answer: (i) Graph A represent D.C. and graph B represent A.C.
(ii) Source of (A) – Dry cell
Source of (B) – A.C. generator
(iii) For graph (B) f = I/T = 1/0.02
f = 50Hz
(iv) 1

Question. Draw a labelled diagram of an electric motor. Explain its principle and working.
What is the function of split ring in an electric motor?
Answer: Electric motor labelled diagram of an electric motor is as follows:
Principle: A current-carrying conductor, when placed in a magnetic field, experiences a force. If the direction of magnetic field and that of current are mutually perpendicular then
force acting on the conductor will be perpendicular to both and will be the given by Fleming’s left-hand rule. Due to this force the conductor begins to move, if it is free to rotate.
Working: Let the current in the coil ABCD of motor enters from the source battery through the conducting brush X, flow along ABCD and finally flows back to the battery through brush
Y. On applying Fleming’s left-hand rule we find that force acting on arm AB due to magnetic field pushes it downwards. But the force acting on arm CD pushes it upwards. Thus, the coil
and the axle rotate anticlockwise. Due to action of split rings P and Q change their contacts with brushes. Now, P makes contact with Y and Q with X. As a result, Current begins to flow in coil along DCBA. The arms are pushed in opposite direction and coil continues to rotate in same direction.

Question. Explain the principle, construction and working of an electric motor with a help of labeled diagram?
Answer: Principle – it is based on the principal that a current carrying conductor placed perpendicular to the magnetic field experiences a force.
Construction-
(i) Armature or coil- It consist of an insulated copper wire wound on a soft iron core.
(ii) Strong field magnet- two pole pieces of a strong magnet provides a strong magnetic field.
(iii) Split ring- it consist of two halves(R1 and R2) of a metallic ring which reverses the direction of the current in a coil.
(iv) Brushes- two carbon brushes touch the commutator (split ring).
(v) Battery – a battery is connected across the carbon brushes.

Question. Describe in short an activity to:
a. demonstrate the pattern of magnetic field lines around a straight current carrying conductor, and
b. find the direction of magnetic field produced for a given direction of current in the conductor.
Name and state the rule to find the direction of magnetic field associated with a current carrying conductor. Apply this rule to determine the direction of the magnetic field inside and outside a current carrying circular loop lying horizontally on a table. Assume that the current through the loop is anticlockwise.
Answer:
(a) Fix a cardboard and pass through its centre a thick copper wire AB connected with a cell of 12 V through a rheostat, an ammeter and plug key as shown in figure. Sprinkle the iron filings uniformly on the cardboard. Plug in the key, tap the cardboard gently a number of times. Iron filings align themselves in a pattern of concentric circles around the copper wire, which represents the magnetic field lines.

(b) The direction of magnetic field so produced around a current carrying conductor can be find with the help of a magnetic compass. When we put a magnetic compass at any point of these field fines it get deflected. The direction of deflection of the compass needle is the direction of magnetic field.

If the direction of current is reversed the direction of magnetic field is also reversed. The direction of magnetic field can be found by using Ampere’s right hand thumb rule. According to it, if we hold a straight conductor in our right hand such that thumb points the direction of current in the conductor .

Question. In our daily life we use two types of electric current whose current-time graphs are given below:

a. Name the type of current in two cases.
b. Identify any one source for each type of current.
c. What is the frequency of current in case (b) in our country?
d. On the basis of these graphs list two differences between the two currents.
e. Out of the two which one is used in transmitting electric power over long distances and why?
Answer:
a. (i) DC (ii) AC

b. (i) cell, (b) AC generator
c. 50 c/s or 50 Hz.
d. (i) Magnitude of DC is constant magnitude of AC is varying
(ii) DC is unidirectional ac changes its direction after a fixed period.
e. AC can be transmitted by changing it at high voltage with the help of transformer to minimise loss in transmission.

Question. (a) Describe an experiment with a diagram to show that force is exerted on a current carrying conductor when placed perpendicular in a magnetic field.
(b) How will this force change if current in the conductor is increased?
(c) Name a device that uses the above principle.
Answer:
a. Take a small metal rod AB and suspend it from a stand with the help of two connected wire. Put the rod in between the horse shoe magnet in such a way that rod remains in between the two poles. Pass the current in the rod through the two wires.
You would find that the rod is deflected towards the left. Now reverse the direction of current the rod is deflected in opposite direction. This shows that a force is experienced by a current carrying conductor in magnetic field.
b. If the current in the conductor is increased then more force will act on the rod, and get more deflected.
c. Electric motor.

Question. (a) Explain what is the difference between direct current and alternating current? Write one important advantage of using alternating current.
(b) An air conditioner of 2 kW is used in an electric circuit having a fuse of 10 A rating. If the potential difference of the supply is 220 V, will the fuse be able to withstand, when the air conditioner is switched on? Justify your answer.
Answer:
(a) Direct current is a unidirectional current with constant magnitude. Alternating current is a current which change its magnitude and direction after a fixed period. AC voltage can be increased or decreased. Where is dc voltage cannot be increased or decreased. AC can be transmitted to long distances with lesser power loss.
(b) Given P = 2 kW and V = 200 volt, 
Power, P = VI ⇒ I = p/v
I = 2000/220 = 9.09 A
The rating of the fuse wire is 10 A which is greater than current drawn by air conditioner so when air conditioner is switched on, fuse will not blow off

Question. (a) What is meant by a ‘magnetic field’?
(b) How is the direction of magnetic field at a point determined?
(c) Describe an activity to demonstrate the direction of the magnetic field generated around a current carrying conductor.
(d) What is the direction of magnetic field at the centre of a current carrying circular loop?
Answer:
a. Magnetic field is the space around a magnet or a current carrying conductor in which its magnetic force can be experienced.
b. A magnetic compass is used to demonstrate the direction of the magnetic field generated around a current carrying conductor.
c. Fix a cardboard and insert a wire to pass through its centre normal to the plane of the card board.
Sprinkle iron filings on card board uniformly. Pass the current in the wire. Tap the cardboard gently.
You will find that iron filings align themselves in the concentric circles around the wire. These circles represents magnetic field lines around the conductor.
d.

At the centre of circular loop, the magnetic field lines are straight.

Question. (a) Which effect of the electric current is utilised in the working of an electrical fuse?
(b) A fuse is connected in series or in parallel in household circuit?
(c) Draw a schematic labelled diagram of a domestic circuit which has a provision of a main fuse, meter, one light bulb and a switch socket.
Answer:
a. Heating effect of current
b. In series in the household circuit
c.

Question. (a) When do we state that an electrical appliance is earthed? Mention the function of earth wire in electric lines. Why is it necessary to earth the electric appliances having metallic body?
(b) Explain what is short circuiting and overloading in an electric supply.
Answer:
(a) When metal body of an electric appliance is connected to a wire which is connected to a metal plate buried deep inside the earth is said to be electrically earthed.
(b) If due to damaged insulation, live wire and neutral wire come in contact with each other then it is said to be short circuiting overloading. A circuit over load occurs when the amount of current flowing through the circuit exceeds the rating of the protective device. Every electric circuit in a wiring system must be protected against overloading. It happens when too many electric appliances are connected into a single socket.

Question. (a) An electric current is passed in a horizontal copper wire from east to west. Explain your observations when a compass needle is placed (i) below this wire, (ii) above the wire. Draw inference from your observations.
(b) List the factors on which the strength of the magnetic field due to a straight conductor carrying current depend. How should these be changed to decrease magnetic field at a point?
Answer:
(a) The direction of deflection of a magnetic compass needle depends upon the direction of the magnetic field at that point. The direction of the magnetic field due to a current carrying wire is given by the right hand screw rule. The direction of magnetic field below and above the wire is opposite so deflection in compass needle changes as well i.e, the deflection is reverse direction.
(b) The factors affecting strength of the magnetic field due to a straight wire carrying current:
1. magnitude of current in the wire α I
2- distance of the point from the wire α 1/I
By decreasing current or increasing the distance of the point from the wire, strength of magnetic field also decreases.

Question. (a) Define electromagnetic induction.
(b) Two coils P and S are wound over the same iron core. Coil P is connected to battery and key the coil S is connected to galvanometer. Draw a suitable diagram of this arrangement and write your observations when:
(i) current in the coil P is started by closing the key.
(ii) current continues to flow in coil P.
(iii) current in coil P is stopped by removing the key.
Explain the reason for such observations.
Answer:
a. The phenomenon by producing a current in a coil by changing magnetic field associated with it or by changing a current in the neighbouring coil is called electromagnetic induction. Current so produced is called induced current.
b. (i) When key K is closed due to increasing current a magnetic field is produced which is changing.
In this changing magnetic field coils is kept so an induced current flow through it, so galvanometer shows a deflection.
(ii) After some time current reaches maximum and becomes constant in P coil. There is no change in current so there is no change in magnetic field associated with coil S and
hence no induced current in coil S. Deflection in galvanometer becomes zero.

(iii) Current becomes zero from maximum in coil P and hence galvanometer shows a deflection but now it is in opposite direction.

Question. Two coils C1 and C2 are wrapped around a nonconducting cylinder. Coil C1 is connected to a battery and key and C2 with galvanometer G. On pressing the key (K), current starts flowing in the coil C1 State your observation in the galvanometer.

a. What key K is pressed on.
b. When current in the coil C1 is switched off.
c. When the current is passed continuously through coil C1.
d. Name and state the phenomenon responsible for the above observation. Write the name of the rule that is used to determine the direction of current produced in the phenomena.
Answer:
a. Induced current in coil C2 is produced so galvanometer shows a deflection.
b. Again galvanometer shows a deflection but in opposite direction to the previous one.
c. There will be no deflection in galvanometer.
d. This phenomenon is called electromagnetic induction. The phenomenon in which a changing magnetic field in a coil induces a current in another coil kept near it. Fleming’s right hand rule is used to find the direction of induced current.

Question. (a) The given figure shows a domestic electric circuit.
Study this circuit carefully. List any two errors in the circuit and justify your answer.

(b) Give one difference between the wires used in the element of an electric heater and in a fuse.
(c) List two advantages of parallel connection over series connection.
Answer:
(a) Errors in the circuit
(i) Fuse wire is connected in neutral wire (N) where as it must be connected in live wire (L).
(ii) Circuit of bulb B2 is incomplete.
(b) Element of electric heater has high resistance and high melting point whereas a fuse wire has high resistance and low melting point.
(c) Advantages of parallel connection over series connection.
(i) In parallel combination if one appliance fails to work others keep working.
(ii) Potential difference across each appliance remains same.

Question. (a) Write the values of the following physical quantities in connection with domestic power supply in our country: (i) potential difference between live wire and neutral wire. (ii) frequency of ac.
(b) Explain the role of the following as safety measure in domestic electric appliance/circuits: (i) earth wire (ii) fuse.
Answer:
(a) (i) 220 V, (ii) 50 Hz
(b) Safety measure in electric appliance/circuits:
(i) Earth wire is a safety device to protect us from electric shock due to leakage of current or faulty electric appliances. An earth wire is a thick copper wire connected to a metal
plate buried deep in the earth. The metallic body of the electric appliance is connected to the earth wire, it provides a low resistance conducting path and leaked current goes to
deep in the earth and human beings do not get a fatal electric shock.
(ii) Fuse: It is also a safety device. It is a wire of an alloy with low melting point. If a current greater than a particular values flows in the circuit it will melt and circuit is broken and
stops power supply in the circuit.

Question. What is a solenoid? Draw the magnetic line of forces for solenoid and a bar magnet. Compare the two and state one similarity.
Answer: A solenoid is a large number of turns of insulated copper wires having shape of a cylinder or helix.
Magnetic field are given in following figures.

(a) Fix a white paper sheet on a drawing board with the help of copper pins. Keep a bar magnet in the centre of the paper and sprinkle some iron filings uniformly around the bar magnet. Tap the board gently. Iron filings arrange themselves in a pattern as shown in figure. These iron filings near the bar magnet align themselves along the magnetic field lines.
(b) A current carrying solenoid behaves as a bar magnet one end of the solenoid behaves like a N pole and another end as S pole like two poles in bar magnet, so the field lines of a solenoid and bar magnet appear same in many ways:
(i) Magnetic lines of force inside the body is strong and uniform.
(ii) In both the cases stronger field exists at the poles compared to the middle part.
Dissimilarities
(i) In bar magnet, the poles are not exactly at the ends of the magnet, in solenoid poles can be considered to be lying at the edges.
(ii) In bar magnet, magnetism is permanent but in solenoid it exists only till there is a current in solenoid.

Question. Answer the following questions:
a. What is the direction of magnetic field lines outside a bar-magnet?
b. Why two magnetic field lines cannot intersect each other?
c. What is indicated by crowding of magnetic field lines in a given region?
d. What is the frequency of ac in India?
e. State one advantage of ac over dc.
Answer:
a. From N pole to S pole
b. If two magnetic field lines would intersect each other then at the point of intersection there would be two different directions of magnetic field which is not possible.
c. Magnetic field strength is more in that region.
d. 50 cycles per sec (c/s) or Hz.
e. AC can be step up for transmission over a longer distances with less power loss.

Question. (a) Draw the pattern of magnetic field lines through a bar-magnet and around a current carrying solenoid.
(b) What is the pattern of magnetic field lines inside the solenoid and what does these indicate?
(c) How can a solenoid be utilised to make an electromagnet? 
(d) State two ways by which the strength of this electromagnet can be increased.
Answer:

(b) These are parallel straight lines indicating that magnetic field is uniform inside the solenoid.
(c) By inserting a soft iron rod into the middle part of solenoid it is used to make an electromagnet
(d) (i) By increasing the number of turns.
(ii) By increasing the strength of current.

Question. With the help of a labelled circuit diagram describe an activity to illustrate the pattern of the magnetic field lines around a straight current carrying long conducting wire.
(i) Name the rule that is used to find the direction of magnetic field associated with a current carrying conductor.
(ii) Is there a similar magnetic field produced around a thin beam of moving:
(a) alpha particles and (b) neutrons? Justify your Answer:
Answer:(i) Take a battery (12 V), a variable resistor (rheostat), an Ammeter (0.5 A), a plug key, a long thick straight copper conducting wire.
(ii) Insert the thick wire through the centre normal to the plane of rectangular cardboard.
(iii) Take care that cardboard is fixed and does not slide up or down.
(iv) Connect the copper wire vertically between points X and Y as shown in diagram in series with battery, plug and a key.
(v) Sprinkle some iron flings unformly on the cardboard.
(vi) Keep the variable resistance in fixed position.
(vii) Close the key so that current flows through the wire.
(viii) Ensure the copper wires placed remains vertically straight.
(ix) Gently tap the iron filings.

Observation:
Iron filings align themselves showing a pattern of concentric circles around the copper wire which represents magnetic lines of force.
(i) Right hand rule.
(ii) (a) Yes, alpha particle being positively charged constitutes a current in the direction of motion.
(b) No, neutrons being electrically neutral constitute no current.

Question. What is meant by magnetic force? Name and explain the rule to determine the direction of force experienced by a current carrying conductor in a magnetic field. How does this force gets affected on:
(i) doubling the magnitude of current, (ii) reversing the direction of flow of current, (iii) reversing the direction of magnetic field.
Answer:The force experienced by a current carrying conductor when placed in a magnetic field or the force experienced by a charged particles moving in a magnetic field is called magnetic force.Fleming left hand rule: According to this rule, on stretching the thumb, forefinger and the middle finger of your left hand such that these are perpendicular to each other, if the force finger points in the direction of magnetic field and middle finger in the direction of current, then the thumb will point in the direction of motion of force acting on the conductor.
(i) If magnitude of current is doubled, then force is doubled.
(ii) If direction of flow of current is reversed, the direction of force is also reversed.
(iii) If direction of magnetic field is reversed, the direction of force is also reversed.