A galvanometer of resistance 50 `Omega` is connected to a battery of 3 V along with a resistance of 2950 `Omega` in series shows full-scale deflection of 30 divisions. The additional series resistance required to reduce the deflection to 20 divisions is

Options

A. `4440 Omega`
B. `1500 Omega`
C. `7400 Omega`
D. `2950 Omega`

Answer

B

Explanation

Let current per division be I
For full scale deflection,
`30I= (3)/(50+2950)= (3)/(3000), I= (1)/(3) xx 10^(-4)A`
When additional series resistance R is connected,
`20I= (3)/(50+2950+ R)implies 20 xx (1)/(3) xx 10^(-4)= (3)/(3000+R)`
`R= 1500 Omega`