A galvanometer coil has a resistance of `15 Omega` and the metre shows full scale deflection for a current of 4 mA. To convert the meter into a voltmeter of range 0 to 18 V, the required resistance is

Options

A. `5885 Omega "in series"`
B. `4485 Omega "in series"`
C. `5885 Omega "in series"`
D. `4485 Omega "in series"`

Answer

B

Explanation

The galvanometer can be transformed into a voltmeter by applying a high resistance in series. If the series resistance is R, then total resistance in cirucit `=(15 + R)Omega`
Now, `15+R = V/I = 18/(4 xx 10^(-3)) = (18 xx 10^(3))/(4) = 4.5 xx 10^(3)`
`therefore R= 4500 - 15= 4495 Omega`