A potentiometer wire has length `4 m` and resistance `8 Omega`. The resistance that must be connected in series with the wire and an accumulator of e.m.f. `2 V`, so as the get a potential gradient `1 mV` per cm` on the wire is

Options

A. `40 Omega`
B. `44 Omega`
C. `48 Omega`
D. `32 Omega`

Answer

D

Explanation

`P.d.` across wire
`=0.1xx=0.4 V`
Current in the circuit
`i=0.4/8=1/20 A`
`i=2/(R+8)`
`1/20=2/(R+8)`
`R= 32 Omega`