Magnetic Effects of Current and Magnetism
Unit 3. Covers Biot-Savart law; Ampere’s law; Force on moving charges and conductors; Current loop as a magnetic dipole; Bar magnet and magnetic materials.
About this unit
This unit connects electricity and magnetism. It shows that moving charges and currents produce magnetic fields (Biot-Savart and Ampere’s laws), that magnetic fields push on moving charges and current-carrying wires, and that a current loop behaves like a small magnet. It ends with bar magnets and how different materials respond to magnetic fields. Motors, meters, loudspeakers and MRI machines all rest on these ideas.
How to prepare
- Memorise the field formulas: loop centre μ₀I/2R, long wire μ₀I/2πr, solenoid μ₀nI.
- Learn F = qvB sin θ and F = BIL sin θ, with Fleming’s left-hand rule.
- Practise galvanometer conversions: shunt for ammeter, series resistance for voltmeter.
- Make a comparison chart of dia-, para- and ferromagnetic materials.
- Remember μ₀ = 4π × 10⁻⁷ T m A⁻¹.
Topics in this chapter
Biot-Savart law
Oersted’s experiment and the field of a circular loop.
6 questionsAmpere’s law
Fields of a long straight wire and a solenoid.
5 questionsForce on moving charges and conductors
Force between parallel currents and the definition of the ampere.
5 questionsCurrent loop as a magnetic dipole
Dipole moment and torque; the moving coil galvanometer, ammeter and voltmeter.
5 questionsBar magnet and magnetic materials
Field of a bar magnet; para-, dia- and ferromagnetism.
5 questions