Multiple Choice Questions
Question. The obstruction offered by material of conductor to the passage of electric current is known as :
(d). None of these
Question. Which of the given statements is true regarding ammeter and voltmeter?
(a). Ammeter is connected in series with the required device, Voltmeter in parallel
(b). Both ammeter and voltmeter are connected in series with required device
(c). The voltmeter is connected in series with the device, Ammeter in parallel
(d). They can be connected in any way
Question. The instrument used for measuring electric current is :
Question. The unit of potential difference is :
Question. Copper is not preferred to make fuse wire because it .
a. is a good conductor of electricity
b. has a low melting point
c. has a high melting point
d. is not easily available
Question. While a cell is being charged, energy is converted into energy.
a. mechanical, electrical
b. electrical, chemical
c. heat, electrical
d. chemical, heat
Question. The unit of resistivity is :
(a) V A
(b) V A
(c) V m /A
Question. Identify the correct circuit diagram:
Assertion-Reason Type Questions
Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Question. Assertion (A) : Longer wires have greater resistance and the smaller wires have lesser resistance.
Reason (R) : Resistance is inversely proportional to the length of the wire.-
Question. Assertion (A) : Tungsten metal is used for making filaments of incandescent lamps.
Reason (R) : The melting point of tungsten is very low.
Question. Assertion (A) : Alloys are commonly used in electrical heating devices, like electrical iron, toasters etc.
Reason (R) : Alloys do not oxidise (burn) readily at high temperatures.
Question. Assertion (A) : Bending a wire does not affect electrical resistance.
Reason (R) : Resistance of a wire is proportional to resistivity of material.
Case Study Based Questions
Electrical resistivities of some substances, at 20°C are given below in the table.
Study the table and answer the given questions.
Question. Which is a better conductor of electric current ?
Question. Which element will be used for electrical transmission lines ?
(D) mercury U
Question. Nichrome is used in the heating elements of electric heating device because:
(A) It has high resistivity
(B) It does not oxidise readily at high temperature
(C) Both of the above
(D) None of the above U
Question. Series arrangement is not used for domestic circuits because:
(A) Current drawn is less
(B) Current drawn is more
(C) Neither of the above
(D) Both of the above U
Short Answer Type Questions
Question. Define the following terms:
(a) one ampere (b) 1 volt.
Answer. Ampere: The SI unit of electric current is ampere (A). One ampere is the electric current when one coulomb of charge flows through a conductor in one second.
Volt: The SI unit of potential difference is volt (V). One volt is the potential difference between two points in an electric circuit when one joule of work is done to move a charge of one coulomb from one point to the other.
Question. Write the factors on which heat produced in a resistor depends
Answer. heat produced in a resistor is directly proportional to
• Square of current (I2)
• Resistance of the resistor (R) and
• Time for which the current flows through the resistor.(t)
H = I2Rt joules
By Ohm’s law, we get H = VIt joules = V2t/R joules
Question. A bulb is rated at 5.0 V, 100 mA. Calculate its (a) power and (b) resistance.
Answer. Rating of bulb, V = 5 0. Volt, I = 100 mA = 100 x10-3A = 0.1A
a. Power of bulb = V x l, P = 5 .0 x 0 .1 = 0.5W
b. V = IR, R =V/l = 5/.1 =50 Ω
Question. Two students perform experiments on series and parallel combinations of two given resistors R1 and R2 and plot the following V-I graphs
Answer. Which of the graphs is (are) correctly labelled in terms of the words ‘Series and parallel’? justify your answer. In case of series combination, the effective resistance = R1 + R2 is more, hence slope of V – I graph will be more. It is otherwise in case of I – V graph. So, series and parallel are correctly marked in graph (ii).
Long Answer Type Questions
Question. What is the better way of connecting lights and other electrical appliances in domestic wiring? Why?
The better way of connecting lights and other electrical appliances in domestic wiring is parallel connection because of the following advantages:
• In parallel circuit, if one appliance stops working due to some defect, then all other appliances keep working normally.
• In parallel circuit, each electrical appliance has its own switch due to which it can be turned on or off, without affecting other appliances.
• In parallel circuit, each electrical appliance gets the same voltage (220V) as that of the power supply line.
• In parallel circuit, the overall resistance of the domestic circuit is reduced due to which the current from the power supply is high.
Question. Distinguish between resistances in series and resistances in parallel.
Answer. Resistances in series:
1. If a number of resistances are connected in such a way that the same current flows through each resistance, then the arrangement is called resistances in series.
2. The current across each resistance is same.
3. The equivalent resistance in series combination is greater than the individual resistances.
4. This combination decreases the current in the circuit.
Resistances in parallel:
1. If a number of resistances are connected between two common points in such a way that the potential differences across each of them is the same, then the arrangement is called resistances in parallel.
2. The voltage across each resistance is same.
3. The equivalent resistance in parallel combination is smaller than each of the individual resistances.
4. This combination increases the current in the circuit.
Question. In the given circuit, A, B, C and D are four lamps connected with a battery of 60 V.
Analyse the circuit to answer the following questions.
(i) What kind of combination are the lamps arranged in (series or parallel)?
(ii) Explain with reference to your above answer, what are the advantages (any two) of this combination of lamps?
(iii) Explain with proper calculations which lamp glows the brightest?
(iv) Find out the total resistance of the circuit R
Answer. (i) The lamps are in parallel.
(ii) Advantages: If one lamp is faulty, it will not affect the working of the other lamps. They will also be using the full potential of the battery as they are connected in parallel.
(ii) The lamp with the highest power will glow the brightest.
P=VI In this case, all the bulbs have the same voltage. But lamp C has the highest current.
Hence, for Lamp C, power P = 5 × 60 Watt = 300 W. (the maximum).
(iii) The total current in the circuit = 3+4+5+3 A = 15A
Voltage = 60V
R = V/I = 60/15 = 4 Ω