Question

A potentiometer wire has length 2 m and resistance 6 ohm. The resistance that must be connected in series with the wire and an accumulator of 2 emf 4 V , so as to get a potential gradient of 1 mV per cm on the wire is-

a) 57
b)32
c) 40
d) 114



The answer is D).. please tell me the method

Answer 1

Answer:

114 ohm(option d) of resistance must be connected in series to get a potential gradient of 1 mV per cm

Explanation:

With a potential gradient of 1 mV per cm, the net voltage across a length of 2m of potentiometer

V = 1 mV/cm x 200 cm = 200 mV = 0.2 V

Given the accumulator voltage is 4 V, this voltage is divided among the potentiometer and the series resistance,

Hence voltage across the potentiometer,

V = (6x4)/(6 + R) = 0.2

=> 24/0.2 = 6 + R

=> 6 + R = 120

=> R = 114

Hence 114 ohm(option d) of resistance must be connected in series to get a potential gradient of 1 mV per cm