Question

A wire of length 100 cm is connected to a cell of emf 2 V and negligible internal resistance. The resistance of the wire is 3Ω. The additional resistance required to produce a potential difference of 1 mV/cm is

(a) 47Ω

(b) 57Ω

(c) 60Ω

(d) 55Ω

Answer 1

The correct option is (b) 57Ω.

Explanation:

Let a resistance R be connected in series with the battery and wire.

Voltage drop across wire

= 1 x 10^-3 x 100

= 0.1 V

Let current in circuit be l

0.1 = l x 3 = 3 x 2/(R+3) 

R = 57 Ω