A `100 V` voltmeter of internal resistance `20 k Omega` in series with a high resistance `R` is connected to a `110 V` line. The voltmeter reads `5 V`, the value of `R` is

Options

A. `210 Omega`
B. `315 Omega`
C. `420 Omega`
D. `400 Omega`

Answer

C

Explanation

(c ) Here `i= (10)/(20 xx 10^(3) + R)`
`:. V = iR implies 5 = ((110)/(20 xx 10^(3) + R)) xx 20 xx 10^(3)`
`implies 10^(5) + 5R = 22 xx 10^(5) implies R = 21 xx (10^(5))/(5) = 420 K Omega`