Question

In a moving coil galvanometer, when the number of turns of the coil is doubled,

• A. both the current sensitivity and voltage sensitivity are doubled
• B. the current sensitivity is halved but voltage sensitivity remains uncharged
• C. the current sensitivity remains unchanged but voltage sensitivity is doubled
• D. the current sensitivity is doubled but voltage sensitivity remains unchanged
• E. both the current sensitivity and voltage sensitivity remain unchanged

Answer 1

The Correct Option is D

In a moving coil galvanometer, the current sensitivity \( S_I \) is directly proportional to the number of turns \( N \) of the coil. The voltage sensitivity \( S_V \) is proportional to the number of turns squared. Therefore, when the number of turns \( N \) of the coil is doubled, the current sensitivity \( S_I \) becomes double, while the voltage sensitivity \( S_V \) remains unchanged. Hence, the correct answer is that the current sensitivity is doubled, but voltage sensitivity remains unchanged.  

The correct option is (D) : the current sensitivity is doubled but voltage sensitivity remains unchanged

Answer 2

In a moving coil galvanometer, the current sensitivity is defined as the deflection per unit current and is given by: 

\( \text{Current Sensitivity} \propto NAB \) where: 

• \( N \) = number of turns
• \( A \) = area of the coil
• \( B \) = magnetic field strength

If the number of turns \( N \) is doubled, the current sensitivity also doubles. 

Voltage sensitivity is defined as the deflection per unit voltage: 
\( \text{Voltage Sensitivity} = \frac{\text{Current Sensitivity}}{R} \), where \( R \) is the resistance of the coil. 

When the number of turns is doubled, the length of the wire increases, so the resistance \( R \) also approximately doubles. Hence: 
- Current sensitivity becomes \( 2 \times \text{original} \) - Resistance becomes \( 2 \times R \) - Voltage sensitivity becomes: 
\( \frac{2 \times \text{original current sensitivity}}{2 \times R} = \text{original voltage sensitivity} \) 

Final Answer: \( \boxed{\text{the current sensitivity is doubled but voltage sensitivity remains unchanged}} \)