Fuse protects circuit by: MCQ with Answer and Explanation

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Fuse protects circuit by:

A. Melting on overcurrent

B. Storing energy

C. Amplifying signal

D. Limiting voltage

Answer: Option A

Solution (By JKSSB Mock Tests)

Fuse wire melts when current exceeds rating (Joule heating I²R), breaking circuit to prevent damage. Sacrificial overcurrent protection. Memory aid: 'Fuse = thermal cutoff; rated current slightly above normal'. Safety device function frequently tested in competitive electricity sections.

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Question #1

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The force on a current-carrying conductor in a magnetic field is maximum when the conductor is

A. At 45°

B. Parallel to field

C. At 60°

D. Perpendicular to field

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Correct Answer: Option D

Explanation:
F = BIL sinθ. Maximum when θ = 90° (sin90°=1), so perpendicular. Parallel (θ=0°) force zero. This is the motor effect, used in electric motor.

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Question #2

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The working of an electric motor is based on

A. Chemical effect of current

B. Magnetic effect of current

C. Electromagnetic induction

D. Heating effect of current

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Correct Answer: Option B

Explanation:
Motor converts electrical to mechanical energy using force on a current-carrying conductor in magnetic field (F = BIL). Electromagnetic induction is for generator. Motor principle: A current-carrying coil experiences torque in magnetic field.

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Question #3

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A tuning fork A produces 5 beats/second with tuning fork B of frequency 256 Hz. If a little wax is applied to fork A, the beat frequency becomes 2 beats/second. The original frequency of fork A was:

A. 251 Hz

B. 254 Hz

C. 261 Hz

D. 258 Hz

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Correct Answer: Option C

Explanation:
The beat frequency is |fA - fB|. So fA is either 256+5=261 Hz or 256-5=251 Hz. Adding wax increases mass, which strictly decreases frequency. If fA was 261, decreasing it brings it closer to 256, reducing beats to 2 (e.g., 258-256=2). If it was 251, decreasing it would increase the beats (e.g., |248-256|=8). Thus, it was 261 Hz.

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