A galvanometer coil has a resistance of 12 Ω and the meter shows full scale deflection for a current of 3mA. It may be converted into a voltmeter of range 0 to 18 V if a resistance of value........  Ω is connected in..........

Given,

Resistance of galvanometer coil, G = 12Ω

Current for which there is full scale deflection

i  = 3mA = 3 × 10^–3 A.

A range of voltmeter is O, which needs to be converted to 18V.

So,

V = 18V

Let  as  a  resistor  of  resistance  R  be  connected  in  series with  the  galvanometer  to  convert  it  into  a  voltmeter. Then,

Then, we can write resistance of series resistor is –

$R=\frac{V}{I_g}-R_G$

$R=\frac{18}{3\times {10}^{-3}}-1\Omega$

$R=5988\Omega$

Hence, converted into a voltmeter of range O to 18V, add resistance of value 5988Ω is connected in series.