JEE Main · 2023 · 31 Jan 2023 · Shift 2 · Current Electricity

The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by

50%

. The percentage change in voltage sensitivity of the galvanometer will be:

(A) $100%$
(B) $50%$
(C) $75%$
(D) $0%$ ✓ Correct

Answer: (D)

Solution

The current sensitivity of the galvanometer is

\frac{N B A}{k}

, rising in proportion to the number of turns

N

. The voltage sensitivity is this divided by the coil resistance,

\frac{N B A}{k R}

. Adding more turns of the same wire lengthens the coil, so its resistance

R

grows in the very same proportion as

N

, and the ratio

\frac{N}{R}

that fixes the voltage sensitivity does not change. However much the current sensitivity is raised, the voltage sensitivity shows no change whatsoever.

JEE Main · 2023 · 31 Jan 2023 · Shift 2 · Single correct option

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