The working principle of an electric generator is: MCQ with Answer and Explanation

The working principle of an electric generator is:
A. Heating effect of current
B. Chemical effect of current
C. Magnetic effect of current
D. Electromagnetic induction
Answer: Option D
Solution (By JKExamLibrary)
Electric generators convert mechanical energy to electrical energy using electromagnetic induction: rotating a coil in magnetic field (or vice versa) induces EMF due to changing magnetic flux. This is Faraday's law application. Motors use the reverse principle (force on current-carrying conductor in field). Memory tip: 'Generator: motion ⇒ electricity (induction); Motor: electricity ⇒ motion (force)'. This application question tests understanding of device principles, common in competitive exams. Always distinguish generator (induction) from motor (Lorentz force) operation.

This question belongs to: Science Physics

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Question #1 Report Error
Free fall: height h takes time t. Height 4h takes time:
A. t/2
B. 4t
C. t
D. 2t

Correct Answer: Option D


Explanation:
h = ½gt² ⇒ t ∝ √h. If h' = 4h, t' = √4 × t = 2t. Time doubles when height quadruples. Memory aid: 'Free fall: t ∝ √h; 4× height ⇒ 2× time'. Kinematics proportionality frequently tested in competitive exams.

This question belongs to: Science Physics
Question #2 Report Error
A piece of ice floats in water with 1/10 of its volume above water. The density of ice is
A. 0.9 g/cm³
B. 0.5 g/cm³
C. 0.8 g/cm³
D. 1.0 g/cm³

Correct Answer: Option A


Explanation:
Fraction of volume submerged = ρ_ice / ρ_water. If 1/10 above, 9/10 submerged. So ρ_ice/ρ_water = 9/10 => ρ_ice = 0.9 g/cm³. Density of ice is 0.9 g/cm³.

This question belongs to: Science Physics
Question #3 Report Error
A body of mass 2 kg is moving with an acceleration of 5 m/s². The rate of change of its momentum is:
A. 0.4 N
B. 10 kg m/s
C. 10 N
D. 2.5 N

Correct Answer: Option C


Explanation:
According to Newton's Second Law of Motion, the rate of change of momentum is directly proportional to the applied unbalanced force. Rate of change of momentum = Force = mass × acceleration. Force = 2 kg × 5 m/s² = 10 Newtons (N). Note that '10 kg m/s' is a unit of momentum, not its rate of change.

This question belongs to: Science Physics