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Electromagnetism — KCSE Physics

KCSE Physics · 109 practice questions · 8 syllabus objectives

38 easy35 medium36 hard

What You'll Learn

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

Explain the working of the electric bell, relay, DC motor, loudspeaker, galvanometer and telephone receiver

Describe the magnetic field around a current-carrying conductor (straight wire, solenoid) and state the right-hand grip rule

Apply Fleming's left-hand rule to determine the direction of force on a current-carrying conductor in a magnetic field

Describe the structure and working principle of an electric motor and a moving-coil loudspeaker

Describe Oersted’s experiment; sketch magnetic field patterns around straight conductors, loops and solenoids; apply the right-hand grip rule

State factors affecting electromagnet strength; explain why soft iron is preferred for cores; describe core shape effects

Apply Fleming’s left-hand rule; explain the catapult effect; determine force direction on a current-carrying conductor; explain force between parallel conductors

Electromagnetism

Sample Questions

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1
easySHORT ANSWER3 marks

Define Fleming’s left-hand rule and explain its application in determining the direction of force on a current-carrying conductor in a magnetic field. (3 marks)

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Part (a) — 1 mark
Fleming’s left-hand rule states that if the thumb, index finger, and middle finger of the left hand are held at right angles to each other, the thumb represents the direction of force, the index finger the direction of the magnetic field, and the middle finger the direction of the current. (1 mk)
Part (b) — 2 marks
To determine the direction of force, align the index finger in the direction of the magnetic field and the middle finger in the direction of the current; the thumb will then point in the direction of the force experienced by the conductor. (1 mk)
This application helps predict the motion of the conductor when it is placed in a magnetic field, crucial for understanding electric motors and other electromagnetic devices. (1 mk)
2
easySHORT ANSWER1 mark

Describe how the shape of the core can affect the strength of an electromagnet. (1 mark)

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Part (a) — 1 mark
A compact or U-shaped core concentrates the magnetic field lines, enhancing the overall strength of the electromagnet (1 mk)
3
easySHORT ANSWER2 marks

Explain why soft iron is considered preferable for use as a core in electromagnets. (2 marks)

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Part (a) — 2 marks
Soft iron has high magnetic permeability, allowing it to be easily magnetised (1 mk)
It demagnetises quickly when the current is switched off, preventing residual magnetism (1 mk)
4

Identify three factors that influence the strength of an electromagnet. (3 marks)

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