Electric motor works on principle of: MCQ with Answer and Explanation

Electric motor works on principle of:
A. Thermal expansion
B. Force on current in magnetic field
C. Electrostatic attraction
D. Electromagnetic induction
Answer: Option B
Solution (By JKExamLibrary)
Motor: current-carrying conductor in magnetic field experiences Lorentz force (F = ILB), causing rotation. Generator uses reverse principle (induction). Memory tip: 'Motor: electricity ⇒ motion (force); Generator: motion ⇒ electricity (induction)'. Device principle question frequently tested in competitive electromagnetism sections.

This question belongs to: Science Physics

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Practice More Physics Questions

Question #1 Report Error
Two waves of identical frequency and amplitude superimpose in the same medium. If they meet perfectly in phase (crest meets crest), the resulting amplitude is:
A. Same as the individual amplitude
B. Zero
C. Four times the individual amplitude
D. Twice the individual amplitude

Correct Answer: Option D


Explanation:
This is an example of constructive interference. According to the principle of superposition, the resultant displacement is the algebraic sum of individual displacements. If the waves are perfectly in phase, their amplitudes add directly (A + A = 2A). Note that while amplitude doubles, the intensity (which is proportional to amplitude squared) becomes four times greater.

This question belongs to: Science Physics
Question #2 Report Error
The time period of revolution of a geostationary satellite is:
A. 12 hours
B. 84 minutes
C. 24 hours
D. Variable

Correct Answer: Option C


Explanation:
Geostationary satellites orbit in Earth's equatorial plane with period matching Earth's rotation period (24 hours), so they appear stationary relative to ground. Orbital radius is about 42,000 km from Earth's center. Memory tip: 'Geostationary: T=24 h, equatorial orbit, fixed position; used for communication/weather satellites'. This standard result is frequently tested in competitive exams. Always recall that geostationary is a special case of geosynchronous (same period) with zero inclination; competitive exams often compare low orbit (84 min) vs geostationary (24 h) periods.

This question belongs to: Science Physics
Question #3 Report Error
One micron is equal to
A. 10⁻³ m
B. 10⁻¹⁰ m
C. 10⁻⁶ m
D. 10⁻⁹ m

Correct Answer: Option C


Explanation:
Micron or micrometer = 10⁻⁶ m.

This question belongs to: Science Physics