Electromagnetism: Paper 3 Guide (Form 5 SPM Physics)

Paper 3 at a glance

• Paper 3 carries 15 marks

Experiment: The effect on a current-carrying conductor in a magnetic field

To study the force that acts on a current-carrying conductor placed in a magnetic field and how it depends on the direction of the current and the field.

• Manipulated: Direction of the current (and of the magnetic field)
• Responding: Direction in which the conductor moves
• Constant: The magnetic field strength and the conductor used
• Graph: No graph is needed because the results are qualitative. The observations are compared with Fleming's left-hand rule.
• Analysis: A current-carrying conductor in a magnetic field experiences a force produced by the interaction (catapult) of the two fields. Its direction is given by Fleming's left-hand rule; reversing the current or the field reverses the force.

• Full experiment page

Experiment: Factors affecting the force on a current-carrying conductor

To investigate how the magnitude of the force on a current-carrying conductor in a magnetic field depends on the current.

• Manipulated: Current in the conductor, I
• Responding: Force on the conductor (shown by the change in the balance reading)
• Constant: The magnetic field strength and the length of the conductor in the field
• Graph: Plot F (y-axis) against I (x-axis). A straight line through the origin shows the force is directly proportional to the current.
• Analysis: The force is given by F = BIl. When B and l are constant, F is directly proportional to I, and the gradient of the F against I graph equals Bl.

• Full experiment page

Paper 3 skill checklist

• Table: quantities with units in the headings, consistent decimal places, derived column calculated correctly.
• Graph: axes labelled with unit, scale using more than half the grid, points plotted with a sharp pencil, best-fit line.
• Gradient: a large triangle on the line, coordinates shown, unit of the gradient stated.
• Relationship: "y increases linearly with x" or "y is directly proportional to x" only if the line passes through the origin.
• Precaution: one that improves accuracy, stated with its reason.

More on graph skills

• Graph skills hub
• All Paper 3 experiments

More Electromagnetism resources

• Chapter overview: Electromagnetism
• Revision Notes
• Common Mistakes
• Practice Questions
• Paper 2 Answering 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)