Question

A moving coil galvanometer of resistance \(100\,\Omega\) shows a full scale deflection for a current of \(1\,\text{mA}\). The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of \(5\,\text{mA}\), is ________ \(\Omega\).

• A. 25
• B. 2.5
• C. 10
• D. 0.5

Hint:

To convert a galvanometer into an ammeter, always connect a low resistance shunt in parallel.

Answer 1

The Correct Option is A

Step 1: Identify given quantities.
Galvanometer resistance, \(G = 100\,\Omega\)
Galvanometer full scale current, \(I_g = 1\,\text{mA}\)
Required full scale current, \(I = 5\,\text{mA}\)
Step 2: Use formula for shunt resistance.
\[ S = \frac{G I_g}{I - I_g} \]
Step 3: Substitute values.
\[ S = \frac{100 \times 1}{5 - 1} = \frac{100}{4} = 25\,\Omega \]