Question

A miliammeter of resistance 5 ohms gives a full scale deflection for a current of 15 mA. If the milliammeter is to be used to measure currents upto 1.5 A the size of the resistance that must be attached to the milliammeter is

• A. 0.0505 ohm
• B. 0.505 ohm
• C. 0.05 ohm
• D. 505 ohm

Answer 1

Answer: (A)

0.0505 ohm

$\text{Resistance of shunt:}S=\frac{R_g{I}_g}{I-I_g}$

$\text{Here,}{R}_g=5\Omega ,I_g=0.015\text{A},I=1.5\text{A}$

$\Rightarrow S=\frac{5\times 0.015}{1.5-0.015}=\frac{5}{99}$

$\Rightarrow S=0.0505\Omega$