JEE Physics Current Electricity MCQs Set B

Question. Five cells each of emf E and internal resistance r are connected in series. Due to oversight one cell is connected wrongly. The equivalent internal resistance of the combination is
(a) 5r
(b) 4r
(c) 2r
(d) 3r

Answer: A

Question. Ten identical cells connected in series are needed to heat a wire of length one meter and radius 'r' by 10ºC 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) 10
(c) 30
(d) 40

Answer: A

Question. If voltage across a bulb rated 220 volt - 100 watt drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is
(a) 5%
(b) 10%
(c) 20%
(d) 2.5%

Answer: A

Question. A milli voltmeter of 25 milli volt range is to be converted into an ammeter of 25 ampere range. The value (in ohm) of necessary shunt will be
(a) 0.001
(b) 0.01
(c) 0.05
(d) 1

Answer: D

Question. The mobility of charge carriers increases with
(a) Increase in the average collision time
(b) Increase in the electric field
(c) Decrease in the charge of the mobile carriers
(d) Increase in the mass of the charge carriers

Answer: A

Question. A wire of a certain material is stretched slowly by ten percent. It new resistance and specific resistance become respectively
(a) 1.21 times, same
(b) 1.1 times, 1.1 times
(c) 1.2 times, 1.1 times
(d) Both remain the same

Answer: A

Question. Identify the set in which all the three materials are good conductors of electricity?
(a) Cu, Ag and Au
(b) Cu, Si and diamond
(c) Cu, Ge and Hg
(d) Cu, Hg and NaCl

Answer: A

Question. A flow of 10⁷ electrons per second in a conducting wire constitutes a current of
(a) 1.6 × 10^–12 A
(b) 1.6 × 10²⁶ A
(c) 1.6 × 10^–26 A
(d) 1.6 × 10¹² A

Answer: A

Question. Three copper wires have lengths and cross-sectional areas as (/, A), (2l, A/2) and (l/2, 2A). Resistance is minimum in
(a) Wire of cross-sectional area 2A
(b) Wire of cross-sectional area A
(c) Wire of cross-sectional area 1/2 A
(d) Same in all three cases

Answer: A