Magnetism and electromagnetism

Bar magnets

Magnetic forces are strongest at the north and south poles. Two like poles repel each other. Two unlike poles attract eachother. Attraction and repulsion are examples of non contact forces

Permanent and induced magnets

Permanent produces its own magnetic field. Induced becomes a magnet once in a magnetic field- it always causes a force of attraction

Bar magnets

Magnetic forces are strongest at the north and south poles. Two like poles repel each other. Two unlike poles attract eachother. Attraction and repulsion are examples of non contact forces

Permanent and induced magnets

Permanent produces its own magnetic field. Induced becomes a magnet once in a magnetic field- it always causes a force of attraction

4 types of magnetic material

Iron, steel, cobalt, nickel (made into permanent or induced.)

Magnetic field

The force between a magnet and magnetic material is always called one of attraction. The strength of the field depends on the distance from the magnet. The direction of the magnetic field at any point is given by the direction of the force that would act on another North Pole placed at that point.

Current through a wire

When a current flows through a conducting wire, a magnetic field is produced around it. The strength of the magnetic field depends on the current and distance from the wire.

Solenoid

Shaping a wire to form a solenoid increases the strength of a magnetic field created by a current through the wire. It is strong and uniform inside a solenoid.

Transformer

2 coils of wire- primary and secondary. Wrapped around a magnetic iron core. Primary coil is connected to an alternating current. This makes a magnetic field which passes to the secondary coil, induces a potential difference

Iron core

Increases strength of magnetic field.

Transformers only work with AC because we need a changing magnetic field to induce a p.d

DC produces a constant magnetic field do it doesn’t work in transformers

Potential difference

Same no. of coils in primary and secondary meaning that p.d is the same. 100% efficient and no energy is wasted

If there are more coils on one side, the p.d is higher than the other coil

Step up and step down

Step up: primary has lower voltage, secondary has higher → lower current

Step down: higher voltage in primary coils, lower voltage in secondary coils → higher current