Question

A galvanometer of resistance $50\text{ }\Omega$ has $30$ divisions and a current sensitivity of $1\text{ mA/div}$. What should be the shunt resistance so that it can be converted into an ammeter of range $10\text{ A}$?

• A. $3.15\text{ }\Omega$
• B. $1.55\text{ }\Omega$
• C. $0.15\text{ }\Omega$
• D. $2.50\text{ }\Omega$

Hint:

Since $I_g$ ($0.03\text{ A}$) is extremely small compared to the target range $I$ ($10\text{ A}$), you can approximate the denominator $(I - I_g) \approx I$. This simplifies the calculation to $S \approx \frac{I_g \cdot G}{I} = \frac{1.5}{10} = 0.15\text{ }\Omega$, giving the answer instantly.

Answer 1

The Correct Option is C