Electromagnetic induction — KCSE Physics

KCSE Physics · 118 practice questions · 10 syllabus objectives

31 easy48 medium39 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Describe applications of electromagnetic induction: microphone, induction coil, national grid, high-voltage transmission

State Faraday's law and Lenz's law; explain how a changing magnetic flux induces an EMF

Describe the working principle of an AC generator and state factors that affect the magnitude of induced EMF

Apply the transformer equations (Vp/Vs = Np/Ns and Vp×Ip = Vs×Is for 100% efficiency) to solve transformer problems

State Faraday's and Lenz's laws of electromagnetic induction; describe experiments to demonstrate them

Explain mutual induction and its effects in coupled coils

Identify parts of AC and DC generators; explain operation and sketch output waveforms

State and apply Fleming's right-hand rule to determine direction of induced current

Explain transformer operation, calculate turns/voltage ratios, determine efficiency, and describe methods of reducing energy losses

Electromagnetic induction

Sample Questions

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1
easySHORT ANSWER4 marks

A transformer has a primary coil with 200 turns and a secondary coil with 50 turns. (a) Calculate the turns ratio of the transformer. (2 marks) (b) If the primary voltage is 240 V, determine the secondary voltage. (2 marks)

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Part (a) — 2 marks
Turns ratio = Np / Ns = 200 / 50 (1 mk)
Turns ratio = 4:1 (1 mk)
Part (b) — 2 marks
Using the transformer equation Vs = Vp × (Ns/Np) (1 mk)
Vs = 240 V × (50/200) = 60 V (1 mk)
2
easySHORT ANSWER2 marks

State two factors that affect the magnitude of induced EMF in an AC generator. (2 marks)

View Marking Scheme
Part (a) — 2 marks
The strength of the magnetic field (1 mk)
The speed of rotation of the coil (1 mk)
3
easySHORT ANSWER2 marks

State the principle of operation of an AC generator. (2 marks)

View Marking Scheme
Part (a) — 2 marks
An AC generator converts mechanical energy into electrical energy (1 mk)
by using electromagnetic induction through the rotation of a coil in a magnetic field (1 mk)
4

State Faraday's law of electromagnetic induction. (2 marks)

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