Question

A moving coil galvanometer has $150$ equal divisions. Its current sensitivity is $10-\text{divisions per milliampere}$ and voltage sensitivity is $2\text{divisions per millivolt}.$ In order that each division reads $1\text{volt},$ the resistence in ohms needed to be connected in series with the coil will be

• A. $103$
• B. $10$
• C. $9995$
• D. $99995$

Answer 1

The correct option is C $9995$

Resistance of Galvanometer,

$G=\frac{\text{Current sensitivity}}{\text{Voltage sensitivity}}\Rightarrow G=\frac{10}{2}=5\Omega$

Here $i_g=$ Full scale deflection current

$=\frac{150}{10}=15mA$

$V=$ voltage to be measured $=$ 150 volts
(such that each division reads 1 volt)

$\Rightarrow R=\frac{150}{15\times {10}^{-3}}-5=9995\Omega$