Magnetism

Orientation

Lesson goal: describe magnetic fields and field patterns around magnets, straight wires, coils, solenoids, and electromagnets.

Direction rules matter. A correct answer should state both the rule used and the resulting field direction.

Core Content

Magnetic fields exert forces on magnetic materials and moving charges. Around a current-carrying wire, the magnetic field forms circular loops. Around a solenoid, the field resembles a bar magnet and is strengthened by more turns, greater current, and a suitable core.

Useful force relations:

$$F = BIL\sin\theta$$

$$F = qvB\sin\theta$$

Situation	Direction rule
straight current-carrying wire	right-hand grip rule
solenoid	curled fingers show current, thumb points north pole
force on current in field	relevant motor-effect hand rule if introduced

Concept Check

Around a straight current-carrying wire, magnetic field lines are:
- A. circular around the wire
- B. straight away from the wire only
- C. absent
- D. always vertical
Answer: A.
A solenoid's field is strengthened by:
- A. reducing current to zero
- B. increasing turns or current
- C. removing all coils
- D. using no core under any condition
Answer: B.
Magnetic force on a moving charge is greatest when velocity is:
- A. parallel to the field
- B. perpendicular to the field
- C. zero
- D. unrelated to field direction
Answer: B.

Applied Practice

A 0.30 m wire carries 4.0 A perpendicular to a 0.20 T magnetic field. Find the magnetic force.

$$F = BIL\sin\theta = 0.20\times4.0\times0.30\times\sin90^\circ$$

$$F = 0.24\ \text{N}$$

Final answer: $0.24\ \text{N}$; force is maximum because the wire is perpendicular to the field.

Deep Practice And Writing

Prompt: explain how an electromagnet can be strengthened and why each change affects the magnetic field.

Tutor Context

Tutor should first check which direction rule the student is using and whether the current direction is conventional current.

Maintenance Loop

Retrieve field pattern around a wire, solenoid field direction, and the condition for maximum magnetic force.

Source Trace

This lesson is materialised from the eduKG custom Year 11 chapter, existing textbook section, roadmap lesson, and Module 4 sequence listed in source_refs.