Question

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

• A. ${10}^3$
• B. ${10}^5$
• C. $99995$
• D. $9995$

Answer 1

The correct option is D $9995$

Given data

Current Sensitivity $=10$ division per $mA$

$\therefore I_g=\frac{150}{10}mA=0.015A$

voltage sensitivity $=2$ division per $mV$

$\therefore V_g=\frac{150}{2}mV=0.075mV$

$Rg=\frac{V_g}{I_g}=\frac{0.075}{0.015}=5v$

$v=150\times 1=150\Omega =$ full scale detection

series resistance $R$

$R=\frac{V}{I_g}-R_g=\frac{150}{0.015}-5=9995\Omega$

$\therefore R=9995\Omega$