Electromagnetism: Paper 2 Answering Guide (Form 5 SPM Physics)

Paper 2 at a glance

• Section B: 2 items worth 20 marks, answer one

"Define" items from this chapter

One precise sentence each; the unit is part of the definition where there is one.

• Faraday's law of electromagnetic induction, The magnitude of the induced electromotive force is directly proportional to the rate of change of magnetic flux linking the conductor.
• Magnetic field, The region around a magnet or current-carrying conductor in which a magnetic force can be detected.
• Electromagnet, A magnet made by passing an electric current through a coil, usually wound around a soft iron core, whose magnetism can be switched on and off.
• Force on a current-carrying conductor, The force experienced by a current-carrying conductor placed in a magnetic field, at right angles to both the current and the field.
• Electromagnetic induction, The production of an electromotive force in a conductor when there is a changing magnetic field linking it.
• Induced current, The current that flows in a closed conductor as a result of electromagnetic induction.

"Explain" items from this chapter

Give the physics reason, not a description. Model answers in one breath:

• How an electric motor turns, A current-carrying coil in a magnetic field feels a turning force. Because the two sides of the coil are pushed in opposite directions, the coil spins, and this drives the motor.
• How a transformer changes voltage, A changing current in one coil creates a changing magnetic field that induces a voltage in a second coil. The ratio of turns on the two coils sets how much the voltage is stepped up or down.
• How a generator induces current, Moving a coil in a magnetic field, or moving a magnet near a coil, induces a voltage. A generator spins a coil so the magnetic field through it keeps changing, driving a current.

"Calculate" items from this chapter

Formula, substitution with units, answer with unit, and the trap examiners set for each one.

• Vp / Vs = Np / Ns, Transformer turns ratio, Vp = primary voltage (V); Vs = secondary voltage (V); Np = number of primary turns (no unit) (); Ns = number of secondary turns (no unit) () · The voltage ratio equals the turns ratio. More turns on the secondary means a step-up transformer.
• VpIp = VsIs, Ideal transformer (power), Vp = primary voltage (V); Ip = primary current (A); Vs = secondary voltage (V); Is = secondary current (A) · This assumes 100% efficiency (input power = output power). Stepping down the voltage steps up the current.
• efficiency = (VsIs)/(VpIp) × 100%, Transformer efficiency, Vs = secondary voltage (V); Is = secondary current (A); Vp = primary voltage (V); Ip = primary current (A) · It is output over input, so efficiency is always ≤ 100%. Use power (V × I) values, not voltage alone.

Other command words

• Describe, say what happens, in order, with the observable evidence; keep "why" for an explain mark.
• Sketch, axes labelled with units, the shape that matters (curve vs straight line, intercept, origin), no plotted numbers needed.

Where the marks are in this chapter

The 3 content standards of Electromagnetism can each be asked as a definition, an explanation, a calculation or a diagram. We do not predict which will appear, prepare all of them.

• 4.1 Force on a Current-carrying Conductor in a Magnetic Field
• 4.2 Electromagnetic Induction
• 4.3 Transformer

A three-step answer routine

1. Count the marks: one idea per mark, so a 3-mark explain needs three physics statements.
2. Name the quantity and its symbol before you use it.
3. Re-read the stem for a hidden condition (constant temperature, uniform acceleration, smooth surface).

More Electromagnetism resources

• Chapter overview: Electromagnetism
• Revision Notes
• Common Mistakes
• Practice Questions
• Paper 3 Guide
• Key Terms
• Calculation practice sets

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)