CBSE Class 12 Physics Current Electricity Worksheet Set B

1. What are the factors on which the resistance of a conductor depends? give the corresponding relation.

2. Name two physical conditions on which the resistivity of a metal depends.

3. Define electrical resistivity of a material.

4. How resistivity of f material depends on its conductivity?

5. Two wires of equal length, one of copper and the other of manganin, have the resistance. Which wire is thicker?

6. Define mobility of charge carriers. Give its S.I. unit.

7. A carbon resistor of 47 k  is to be marked with rings of different colours for its identification. write the sequence of the colours.

8. A copper wire of resistivity  is stretched to reduce its diameter to half of its previous value. What will be its resistivity?

9. The variation of potential difference with length in case of two potentiometers A and B is given below. Which of the two is more sensitive and why?

10. Give reason why the electrical conductance of an electrolyte is less than that of metals.

11. If the length of a wire conductor is doubled by stretching it, keeping the potential difference across it constant, by what factor does the drift speed of electrons change?

12. State the condition in which terminal voltage across a stationary cell is equal to its e.m.f.

13. If temperature of a good conductor increases, how does the relaxation time of electrons in the conductor change?

14. You are asked to measure emf of a cell. Which instrument will you use? A high resistance voltmeter or potentiometer and why?

15. Two 120 V light bulbs, one of 25 W and other of 200 W are connected in series. One bulb burnt out almost instantaneously. Which one was burnt out and why?

16. V.I. graph for a metallic wire of two different temperatures T1 & T2 is shown in the figure. Which of the two temperatures is higher and why?

17. State Joule’s Law of Heating.

18. Draw V-I graph for ohmic and non-ohmic materials. Give one example of each.
 

Important Questions for NCERT Class 12 Physics Current Electricity

Question. Faraday law of electrolysis indirectly shows   
(a) quantisation of charge 
(b) quantisation of angular momentum
(c) quantisation of current
(d) quantisation of viscosity

Answer  A

Question. If power dissipated in the 9 W resistor in the circuit shown is 36 watt, the potential difference across the 2 W resistor is   
(a) 4 volt
(b) 8 volt
(c) 10 volt
(d) 2 volt

Answer  C

Question. When a wire of uniform cross-section a, length l and resistance R is bent into a complete circle, resistance between any two of diametrically opposite points will be    
(a) R/4
(b) 4R
(c) R/8
(d) R/2 

Answer  A

Question. Resistance n, each of r ohm, when connected in parallel give an equivalent resistance of R ohm. If these resistances were connected in series, the combination would have a resistance in ohms, equal to   
(a) n2R
(b) R/n2
(c) R/n
(d) nR 

Answer  A

Question. When three identical bulbs of 60 watt, 200 volt rating are connected in series to a 200 volt supply, the power drawn by them will be   
(a) 60 watt
(b) 180 watt
(c) 10 watt
(d) 20 watt 

Answer  D

Question. A wire of length L is drawn such that its diameter is reduced to half of its original diameter. If the initial resistance of the wire were 10 W, its new resistance would be :   
(a) 40 W
(b) 80 W
(c) 120 W
(d) 160 W

Answer  D

Question. Two 220 volt, 100 watt bulbs are connected first in series and then in parallel. Each time the combination is connected to a 220 volt a.c. supply line. The power drawn by the combination in each case respectively will be   
(a) 50 watt, 100 watt
(b) 100 watt, 50 watt
(c) 200 watt, 150 watt
(d) 50 watt, 200 watt 

Answer  D

Question. An electric kettle has two heating coils. When one of the coils is connected to an a.c. source, the water in the kettle boils in 10 minutes. When the other coil is used the water boils in 40 minutes. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be    
(a) 8 minutes
(b) 4 minutes
(c) 25 minutes
(d) 15 minutes

Answer  A

Question. Three equal resistors connected in series across a source of e.m.f. together dissipate 10 watt of power.   
What will be the power dissipated in watt if the same resistors are connected in parallel across the same source of e.m.f.?
(a) 30
(b) 10/3
(c) 10
(d) 90

Answer  D

Question. If two bulbs, whose resistances are in the ratio of 1 : 2 are connected in series, the power dissipated in them has the ratio of   
(a) 2 : 1
(b) 1 : 4
(c) 1 : 1
(d) 1 : 2.

Answer  D

Question. The internal resistance of a cell of e.m.f. 2 V is 0.1 W.    
It is connected to a resistance of 3.9 W. The voltage across the cell will be
(a) 1.95 V
(b) 1.9 V
(c) 0.5 V
(d) 2 V 

Answer  A

Question. A battery of e.m.f 10 V and internal resistance 0.5 W is connected across a variable resistance R. The value of R for which the power delivered in it is maximum is given by   
(a) 0.5 W
(b) 1.0 W
(c) 2.0 W
(d) 0.25 W

Answer  A

Question. Ten identical cells connected in series are needed to heat a wire of length one meter and radius ‘r’ by 10°C in time ‘t’. How many cells will be required to heat the wire of length two meter of the same radius by the same temperature in time ‘t’?    
(a) 20
(b) 30
(c) 40
(d) 10

Answer  A

Question. Two cells, having the same e.m.f. are connected in series through an external resistance R. Cells have internal resistances r1 and r2 (r1 > r2) respectively.
When the circuit is closed, the potential difference across the first cell is zero. The value of R is    
(a) r₁ + r₂
(b) r₁ – r₂
(c) r₁ + r₂ /2
(d) r₁ - r₂ /2

Answer  B

Question. Two identical batteries each of e.m.f 2 V and internal resistance 1 W are available to produce heat in an external resistance by passing a current through it.
The maximum power that can be developed across R using these batteries is  
(a) 3.2 W
(b) 2.0 W
(c) 1.28 W
(d) 8/9 W

Answer  B

Question. The magnitude and direction of the current in the circuit shown will be:

a. 7/3 A from a to b through e
b. 7/3 A from b and a through e
c. 1.0 A from b to a through e
d. 1.0 A from a to b through e
Answer : D

Question. Figure represents a part of the closed circuit. The potential difference between points A and B (VA – VB) is:

a. + 9 V
b. – 9 V
c. + 3 V
d. + 6 V
Answer : A

Question. In the following circuit E₁ = 4V, R₁ = 2Ω, E₂ = 6V, R₂ = 2Ω and R₃ = 4Ω. The current i1 is:

a. 1.6 A
b. 1.8 A
c. 2.25 A
d. 1 A
Answer : B

Question. Determine the current in the following circuit:

a. 1 A
b. 2.5 A
c. 0.4 A
d. 3 A
Answer : A

Question. A battery with negligible internal resistance is connected with 10m long wire. A standard cell gets balanced on 600 cm length of this wire. On increasing the length of potentiometer wire by 2m then the null point will be displaced by:
a. 200 cm
b. 120 cm
c. 720 cm
d. 600 cm
Answer : B

Question. In the following circuit a 10 m long potentiometer wire with resistance 1.2 ohm/m, a resistance R1 and an accumulator of emf 2 V are connected in series. When the emf of thermocouple is 2.4 mV then the deflection in galvanometer is zero. The current supplied by the accumulator will be:

a. 4 × 10^–4 A
b. 8 × 10^–4 A
c. 4 × 10^–3 A
d. 8 × 10^–3 A
Answer : A

Question. The figure shows a network of currents. The magnitude of current is shown here. The current i will be:

a. 3 A
b. 13 A
c. 23 A
d. – 3 A
Answer : C

Question. In an experiment to measure the internal resistance of a cell by potentiometer, it is found that the balance point is at a length of 2 m when the cell is shunted by a 5 Ω resistance; and is at a length of 3 m when the cell is shunted by a 10 Ω resistance. The internal resistance of the cell is, then:
a. 1.5 Ω
b. 10 Ω
c. 15 Ω
d. 1 Ω
Answer : B

Question. A deniel cell is balanced on 125 cm length of a potentiometer wire. When the cell is short circuited with a 2 # resistance the balancing length obtained is 100 cm. Internal resistance of the cell will be:
a. 1.5 Ω
b. 0.5 Ω
c. 1.25 Ω
d. 4/5 Ω
Answer : B

Question. The resistivity of a potentiometer wire is 40 × 10^–8 Ωm and its area of cross section is 8 × 10^–6 m². If 0.2 amp. Current is flowing through the wire, the potential gradient will be:
a. 10^–2 volt/m
b. 10^–1 volt/m
c. 3.2 × 10^–2 volt/m
d. 1 volt/m
Answer : A

Question. When a potential difference is applied across, the current passing through:
a. an insulator at 0 K is zero
b. a semiconductor at 0 K is zero
c. a metal at 0 K is finite
d. a p-n diode at 300 K is finite, if it is reverse biased
Answer : A, B, D

Question. A potentiometer wire of length 10 m and a resistance 30 Ω is connected in series with a battery of emf 2.5 V and internal resistance 5 # and an external resistance R. If the fall of potential along the potentiometer wire is 50 μV/mm, the value of R is: (in Ω)
a. 115
b. 80
c. 50
d. 100
Answer : A

Question. A 2 volt battery, a 15 Ω resistor and a potentiometer of 100 cm length, all are connected in series. If the resistance of potentiometer wire is 5 Ω, then the potential gradient of the potentiometer wire is:
a. 0.005 V/cm
b. 0.05 V/cm
c. 0.02 V/cm
d. 0.2 V/cm
Answer : A

Question. A micro ammeter has a resistance of 100 Ω and full scale range of 50μA. It can be used as a voltmeter or as a higher range ammeter provided a resistance is added to it. Pick the correct range and resistance combination(s):
a. 50 V range with 10 kΩ resistance in series
b. 10 V range with 200 kΩ resistance in series
c. 5 mA range with 1 Ω resistance in parallel
d. 10 mA range with 1 Ω resistance in parallel
Answer : B, C

Question. Heater of an electric kettle is made of a wire of length L and diameter d. It takes 4 minutes to raise the temperature of 0.5 kg water by 40 K. This heater is replaced by a new heater having two wires of the same material, each of length L and diameter 2d. The way these wires are connected is given in the options. How much time in minutes will it take to raise the temperature of the same amount of water by 40 K?
a. 4 if wires are in parallel
b. 2 if wires are in series
c. 1 if wires are in series
d. 0.5 if wires are in parallel
Answer : C, D

Question. Capacitor C₁ of capacitance 1μF and capacitor C₂ of capacitance 2μF are separately charged fully by a common battery. The two capacitors are then separately allowed to discharge through equal resistors at time t = 0:
a. The current in each of the two discharging circuits is zero at t = 0
b. The currents in the two discharging circuits at t = 0 are equal but not zero
c. The currents in the two discharging circuits at t = 0 are unequal
d. Capacitor C_1, loses 50% of its initial charge sooner than C₂ loses 50% of its initial charge
Answer : B, D

Question. For the circuit shown in the figure:

a. the current I through the battery is 7.5 mA
b. the potential difference across R_L is 18 V
c. ratio of powers dissipated in R1and R₂ is 3
d. if R₁ are interchanged, magnitude of the power dissipated in R_L will decrease by a factor of 9
Answer : A, D

Students must free download and practice these worksheets to gain more marks in exams. CBSE Class 12 Physics Worksheet - Current Electricity