Motors & Generators — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Motors & Generators MCQs with step-by-step solutions (5 questions). Part of Electricity & Magnetism. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Motors & Generators · medium · theory
An electric motor converts:
A. electrical energy into mechanical energy ✓ Correct
B. electrical energy into chemical energy
C. mechanical energy into electrical energy
D. heat into electrical energy
Solution: A motor uses the force on a current-carrying coil in a magnetic field to produce rotation (mechanical energy).
Q2 — Motors & Generators · medium · theory
An electric generator (dynamo) converts:
A. chemical energy into heat
B. light into electricity
C. electrical energy into mechanical energy
D. mechanical energy into electrical energy ✓ Correct
Solution: A generator rotates a coil in a magnetic field to induce a current — mechanical to electrical energy.
Q3 — Motors & Generators · hard · theory
The working of an electric generator is based on the principle of:
A. conservation of charge
B. electromagnetic induction ✓ Correct
C. Ohm's law
D. the heating effect of current
Solution: A changing magnetic flux through the coil induces an EMF — electromagnetic induction (Faraday's law).
Q4 — Motors & Generators · medium · theory
An electric generator works on the principle of:
A. chemical reactions
B. electromagnetic induction ✓ Correct
C. static electricity
D. the heating effect of current
Solution: A generator relies on electromagnetic induction: a coil rotating in a magnetic field experiences a changing magnetic flux, which induces an EMF and hence a current.
Q5 — Motors & Generators · hard · theory
A simple electric (DC) motor uses a split-ring commutator. Its main function is to:
A. continuously increase the speed of rotation
B. produce the magnetic field of the motor
C. reduce the current to a safe value
D. reverse the direction of current in the coil every half rotation so the coil keeps turning the same way ✓ Correct
Solution: After every half turn the sides of the coil swap positions between the poles. The split-ring commutator reverses the current in the coil at this instant, so the turning force stays in the same rotational sense and the coil spins continuously.