Understanding magnets, magnetic fields, and how electricity can create motion.
The main magnetic materials are iron, steel, cobalt, and nickel.
Produces its own magnetic field. It can attract or repel other magnets.
Becomes a magnet only when placed in a magnetic field. It only attracts.
The region around a magnet where a force acts on another magnet or magnetic material.
Rule: Magnetic field lines go from North to South outside the magnet, and South to North inside the magnet, forming closed loops.
[Image of magnetic field lines around a bar magnet]Q1: How can you tell the difference between a permanent magnet and a magnetic material (like iron)?
A permanent magnet can repel another magnet; a magnetic material will only ever be attracted.
Q2: Where is the magnetic field strongest?
At the poles (where the field lines are closest together).
When a current flows through a wire, a magnetic field is produced around it.
A coil of wire that produces a strong, uniform magnetic field inside. It is essentially an electromagnet.
Real-world Anchor: Electromagnets in scrap yards are used to pick up cars and then drop them by turning off the current.
[Image of a solenoid magnetic field]To make a solenoid stronger, you can:
1. Increase the current.
2. Increase the number of turns in the coil.
3. Add an iron core.
Q1: Describe the magnetic field inside a solenoid.
The field is strong and uniform (the field lines are parallel).
Q2: Why is an electromagnet often better than a permanent magnet for industry?
Because it can be turned on and off, and its strength can be adjusted.
When a current-carrying wire is placed in a magnetic field, the wire and the magnet exert a force on each other.
$$ F = B \times I \times l $$
What it calculates: Force ($F$) in Newtons.
When it applies: This formula only applies when the wire is fully inside a uniform magnetic field and at right angles to the field.
Common misuse: Using it when the wire is parallel to the field (Force is zero!).
Used to find the direction of the force.
Q1: A wire is parallel to the magnetic field lines. What is the force on it?
Zero. The wire must be at an angle (ideally 90°) to experience a force.
Q2: How can you reverse the direction of the force in a motor?
Reverse the current OR reverse the magnetic field (poles).
If a conductor "cuts" magnetic field lines, a potential difference is induced across the ends of the conductor.
Exam Tip: The faster the conductor cuts the magnetic field lines, the greater the induced potential difference.
A device that changes the magnitude of an alternating potential difference using two coils and an iron core.
$$ V_p \times I_p = V_s \times I_s $$
Note: This relationship assumes an ideal transformer with no energy losses.
Backward Link: This relates to Topic 3 (Electricity) because transformers make power transmission efficient.
Q1: What type of current is required for a transformer to work?
Alternating Current (AC), because it creates a changing magnetic field.
Q2: A step-up transformer has more turns on which coil?
The secondary coil.
1. Don't confuse the Left-Hand Rule (Motors) with the Right-Hand Rule (Generators).
2. Don't say magnetic fields only go N to S; remember they form closed loops.
3. Don't forget that Transformers only work with AC, never DC.