Question

In a moving coil galvanometer if the number of turns increases by 25%, then change in voltage sensitivity is?

• A. 0
• B. 1%
• C. 25%
• D. 50%

Answer 1

The Correct Option is A

The problem asks about the change in voltage sensitivity when the number of turns in a moving coil galvanometer is increased by 25%. To solve this, let's first understand the concept of voltage sensitivity.

Voltage Sensitivity in a moving coil galvanometer is defined as the deflection per unit voltage across the galvanometer. Mathematically, it is given by:

\(S_v = \dfrac{nBA}{k}\)

where:

• \(n\) = number of turns in the coil
• \(B\) = magnetic field strength
• \(A\) = area of the coil
• \(k\) = torque per unit twist of the coil (a constant for the galvanometer)

From this formula, it is clear that voltage sensitivity is proportional to the number of turns \(n\), the magnetic field strength \(B\), and the area \(A\). However, the problem specifies that only the number of turns changes, not the other factors.

However, it is crucial to understand that in practical cases, while the number of turns can be increased, this typically affects the current sensitivity and not the voltage sensitivity because adding more turns and increasing resistance compensates for any theoretical increase in voltage sensitivity.

For this problem, in ideal conditions, if \(n\) (number of turns) increases by 25%, the current sensitivity rather than voltage sensitivity changes. Voltage sensitivity remains unchanged in design, structure, or functional implementation. Therefore, the correct answer is 0% change in voltage sensitivity.

Conclusion: The correct answer is 0. Alterations in the number of turns affect the current sensitivity directly while the voltage sensitivity in ideal cases remains unchanged.