JEE Physics Current Electricity MCQs Set A

Question. Electric current has both magnitude and direction. It is a
(a) Scalar quantity
(b) Tensor quantity
(c) None of these
(d) Vector quantity

Answer: A

Question. Identical piece of Ge and Cu are taken and cooled, then
(a) Resistivity of Cu decreases and Ge increases
(b) Resistivity of both decreases
(c) Resistivity of both increases
(d) Resistivity of Cu increases and Ge decreases

Answer: A

Question. A current of 10 A is maintained in a conductor of cross-section 1 cm². If the number density of free electrons be 9 × 10²⁸ m^–3, the drift velocity of free electrons is
(a) 6.94 × 10^–6 m/s
(b) 5.94 × 10^–2 m/s
(c) 1.94 × 10^–3 m/s
(d) 2.94 × 10^–4 m/s

Answer: A

Question. Ohm's law fails in
(a) All of these
(b) PN junction system
(c) Thyristor
(d) Diode

Answer: A

Question. f a copper wire is stretched to make its radius decrease by 0.1%, then the percentage increase in resistance is nearly
(a) 0.4%
(b) 0.2%
(c) 0.8%
(d) 0.1%

Answer: A

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

Answer: A

Question. The temperature co-efficient of resistance of a wire at 0°C is 0.00125 °C^–1. At 25°C its resistance is one ohm. The resistance of the wire will be 1.2 ohm at
(a) 190°C
(b) 225 K
(c) 260°C
(d) 185 K

Answer: A

Question. A conductor behaves as a superconductor
(a) At critical temperature
(b) At boiling point of that metal
(c) Above critical temperature
(d) At 100°C

Answer: A

Question. A technician has only two resistance coils. By using them singly, in series or in parallel, he is able to obtain the resistance 3, 4, 12 and 16 ohms. The resistance of the two coils are
(a) 4 and 12 ohms
(b) 7 and 9 ohms
(c) 4 and 16 ohms
(d) 6 and 10 ohms

Answer: A

Question. Thousand cells of same emf E and same internal resistance r are connected in series in same order without an external resistance. The potential drop across 399 cells is found to be
(a) Zero
(b) 399 E
(c) 601 E
(d) 1000 E

Answer: A

Question. Five cells each of e.m.f. E and internal resistance r are connected in series. If due to over sight, one cell is connected wrongly, then the equivalent e.m.f. of the combination is
(a) 3 E
(b) 4 E
(c) 2 E
(d) 5 E

Answer: A

Question. Two batteries of different e.m.f.'s and internal resistance connected in series with each other and with an external load resistor. The current is 3.0 A. When the polarity of one battery is reversed, the current becomes 1.0 A. The ratio of the e.m.f.'s of the two batteries is
(a) 2
(b) 2.5
(c) 1.5
(d) 1

Answer: A