CBSE Class 12 Physics Current Electricity Notes and Questions

Question. The potential difference applied to an X-ray tube is 5 KV and the current through it is 3.2 mA. Then the number of electrons striking the target per second is:
a. 2 × 10¹⁶
b. 5 × 10⁶
c. 1 × 10¹⁷
d. 4 × 10¹⁵
Answer : A

Question. A copper wire of length 1m and radius 1mm is joined in series with an iron wire of length 2m and radius 3mm and a current is passed through the wire. The ratio of current densities in the copper and iron wire is:
a. 18 : 1
b. 9 : 1
c. 6 : 1
d. 2 : 3
Answer : B

Question. A conducting wire of cross-sectional area 1 cm2 has 3 × 10²³ m^–3 charge carriers. If wire carries a current of 24 mA, the drift speed of the carrier is:
a. 5 × 10^–6 m/s
b. 5 × 10^–3 m/s
c. 0.5 m/s
d. 5 × 10^–2 m/s
Answer : B

Question. An electron is moving in a circular path of radius 5.1 × 10^–11 m at a frequency of 6.8 × 10¹⁵ revolution/sec. The equivalent current is approximately:
a. 5.1 × 10^–3 A
b. 6.8 × 10^–3 A
c. 1.1 × 10^–3 A
d. 2.2 × 10^–3 A
Answer : C

Question. Two wires of resistance R₁ and R₂ have temperature coefficient of resistance α₁ and α₂ respectively. These are joined in series. The effective temperature co-efficient of resistance is:

Answer : C

Question. A wire of length L and resistance R is stretched to get the radius of cross-section halved. What is new resistance?
a. 5 R
b. 8 R
c. 4 R
d. 16 R
Answer : D

Question. The specific resistance of manganin is 50 x 10^-8 Ωm The resistance of a manganin cube having length 50 cm is:
a. 10^–6 Ω
b. 2.5 × 10^–5 Ω
c. 10^–8 Ω
d. 5 × 10^–4 Ω
Answer : A

Question. Two wires A and B of the same material, having radii in the ratio 1 : 2 and carry currents in the ratio 4 : 1. The ratio of drift speeds of electrons in A and B is:
a. 16 : 1
b. 1 : 16
c. 1 : 4
d. 4 : 1
Answer : A

Question. In the figure a carbon resistor has band of different colours on its body. The resistance of the following body is:

a. 2.2 kΩ
b. 3.3 kΩ
c. 5.6 kΩ
d. 9.1 kΩ
Answer : D

Question. In a wire of circular cross-section with radius r, free electrons travel with a drift velocity v, when a current i flows through the wire. What is the current in another wire of half the radius and of the some material when the drift velocity is 2v?
a. 2i
b. i
c. i/2
d. i/4
Answer : C

Question. A beam of electrons moving at a speed of 10⁶ m/s along a line produces a current of 1.6 × 10^–6 A. The number of electrons in the 1 metre of the beam is:
a. 10⁶
b. 10⁷
c. 10¹³
d. 10¹⁹
Answer : B

Question. The V-i graph for a conductor at temperature T₁ and T₂ are as shown in the figure. (T₂ – T₁) is proportional to:

a. cos 2θ
b. sinθ
c. cot 2θ
d. tanθ
Answer : C

Question. The resistance of a wire at 20°C is 20 Ω and at 500°C is 60Ω. At which temperature resistance will be 25Ω:
a. 50°C
b. 60°C
c. 70°C
d. 80°C
Answer : D

Question. Dimensions of a block are 1 cm × 1 cm × 100 cm. If specific resistance of its material is 3 × 10^–7 ohm-m, then the resistance between it’s opposite rectangular faces is:
a. 3 × 10^–9 ohm
b. 3 × 10^–7 ohm
c. 3 × 10^–5 ohm
d. 3 × 10^–3 ohm
Answer : B

Question. A rod of certain metal is 1 m long and 0.6 cm in diameter. It’s resistance is 3 × 10^–3Ω. A disc of the same metal is 1 mm thick and 2 cm in diameter, what is the resistance between it’s circular faces.
a. 1.35 x 10⁻⁶ Ω
b. 2.7 x 10⁻⁷  Ω
c. 4.05 x 10⁻⁶  Ω
d. 8.1 x 10⁻⁶  Ω
Answer : B

Question. Masses of three wires are in the ratio 1 : 3 : 5 and their lengths are in the ratio 5 : 3 : 1. The ratio of their electrical resistance is:
a. 1 : 3 : 5
b. 5 : 3 : 1
c. 1 : 15 : 125
d. 125 : 15 : 1
Answer : D

Question. A new flashlight cell of emf 1.5 volts gives a current of 15 amps, when connected directly to an ammeter of resistance 0.04 Ω. The internal resistance of cell is:
a. 0.04 Ω
b. 0.06 Ω
c. 0.10 Ω
d. 10 Ω
Answer : B

Question. The temperature co-efficient of resistance of a wire is 0.00125/oC. At 300K. It’s resistance is 1Ω. The resistance of the wire will be 2 Ω at:
a. 1154 K
b. 1127 K
c. 600 K
d. 1400 K
Answer : B

Question. For a cell, the terminal potential difference is 2.2 V when the circuit is open and reduces to 1.8 V, when the cell is connected across a resistance, R = 5Ω. The internal resistance of the cell is:
a. (10/9) Ω
b. (9/10) Ω
c. (11/9) Ω
d. (5/9) Ω
Answer : A

Question. Five resistances are combined according to the figure. The equivalent resistance between the point X and Y will be

a. 10 Ω
b. 22 Ω
c. 20 Ω
d. 50 Ω
Answer : A

Question. An aluminum rod of length 3.14 m is of square crosssection 3.14 × 3.14 mm². What should be the radius of 1 m long another rod of same material to have equal resistance:
a. 2 mm
b. 4 mm
c. 1 mm
d. 6 mm
Answer : C

Question. If a copper wire is stretched to make it 0.1% longer, the percentage increase in resistance will be:
a. 0.2
b. 2
c. 1
d. 0.1
Answer : A

Question. What will be the equivalent resistance of circuit shown in figure between points A and D:

a. 10 Ω
b. 20 Ω
c. 30 Ω
d. 40 Ω
Answer : C

Question. The internal resistance of a cell of emf 2V is 0.1Ω. It’s connected to a resistance of 3.9.Ω The voltage across the cell will be:
a. 0.5 volt
b. 1.9 volt
c. 1.95 volt
d. 2 volt
Answer : C

Question. Two resistance R₁ and R₂ provides series to parallel equivalents as n/1 then the correct relationship is:

Answer : D

Question. In the network shown in the figure each of resistance is equal to 2Ω. The resistance between A and B is:

a. 1 Ω
b. 2 Ω
c. 3 Ω
d. 4 Ω
Answer : B

Please refer to attached file for CBSE Class 12 Physics Current Electricity Notes and Questions