Question

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

• A. (a) 5885 $\Omega$ in series
• A. (b) 4485 $\Omega$ in series
• A. (c) 5885 $\Omega$in parallel
• A. (d) 4485 $\Omega$ in parallel

Answer 1

(b) 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 circuit $= ( 15 + \mathrm { R } ) \Omega$

Now,

$\therefore \mathrm { R } = 4500 - 15 = 4485 \Omega$