Question

There is a galvanometer of resistance $100\Omega$ and full scale current $I_g = 1$ mA. Find shunt resistance required to increase its range to $5$ mA.

• A. $25\Omega$
• B. $0.25\Omega$
• C. $0.5\Omega$
• D. $1\Omega$

Hint:

Shunt resistance is always much smaller than galvanometer resistance.

Answer 1

The Correct Option is A

Step 1: Current through shunt.
\[ I_s = 5 - 1 = 4 \text{ mA} \]
Step 2: Voltage across galvanometer and shunt is same.
\[ I_g G = I_s r_s \]
Step 3: Substituting values.
\[ 1 \times 100 = 4 \times r_s \Rightarrow r_s = \dfrac{100}{4} = 25\Omega \]