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

The working principle of an electric generator is:
A. Electromagnetic induction
B. Heating effect of current
C. Magnetic effect of current
D. Chemical effect of current
Answer: Option A
Solution (By JKSSB Mock Tests)
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.

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Question #1
In simple harmonic motion, acceleration is directly proportional to
A. Square of displacement
B. Displacement but opposite in direction
C. Velocity
D. Time

Correct Answer: Option B


Explanation:
In SHM, a = -ω²x, acceleration ∝ -displacement. Minus sign indicates direction towards mean position (restoring). Characteristic of SHM. Pendulum and spring-mass system exhibit SHM for small displacements.

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Question #2
A lactometer measures
A. Density of milk
B. Viscosity of milk
C. Purity of milk
D. Temperature of milk

Correct Answer: Option C


Explanation:
Lactometer is a type of hydrometer used to check purity of milk by measuring specific gravity. Adulteration with water lowers density. It doesn't measure temperature or viscosity directly.

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Question #3
A vernier caliper has 20 divisions on vernier scale matching 19 main scale divisions. If main scale division is 1 mm, least count is:
A. 0.5 mm
B. 0.05 mm
C. 0.1 mm
D. 0.01 mm

Correct Answer: Option B


Explanation:
Least count = 1 MSD - 1 VSD. 20 VSD = 19 MSD ⇒ 1 VSD = 19/20 mm = 0.95 mm. LC = 1 - 0.95 = 0.05 mm. Formula: LC = MSD/n where n = vernier divisions. Memory tip: LC = smallest measurable difference = main scale value/vernier divisions. Essential for practical physics questions in competitive exams.

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