Magnetism and Electromagnetism

Difference being permanently magnetic and being an induced magnet

Permanent - produces its own magnetic field

Induced - when placed in a magnetic field it temporarily turns into a magnet

Magnetically hard vs Magnetically soft

Soft - easy to magnetise but easily lose their magnetism

Hard - difficult to magnetise but do not easily lose their magnetism Hard

Practical : Investigating magnetic field patterns

1. Place compass at the end of a magnet

2. Mark position at the end of the compass

3. Move the compass to where the needle ended and mark, repeat.

How to produce a uniform magnetic field

- Two permanent magnets

- Arrange them as such that the opposite poles are adjacent

- Place the poles close together

How do loudspeakers work?

1. Alternating current flows through the coil

2. Which induces a changing magnetic field

3. This interacts with the magnetic field of the permanent magnets

4. Due to Flemmings left hand rule a force is acted on the coil causing it to vibrate

5. This causes the cone to oscillate which produces sound wave

How do DC motors work?

1. When the switch is closed there is current in the coil

2. The current in the wires creates a magnetic field around the wires of the coil

3. This magnetic field cuts the field lines created by the permanent magnets

4. This generates a force on the wires of the coil

5. Using Flemming's left hand rule

6. This creates a turning effect on the coil

How to increase the size of an induced voltage

1. Increase speed at which magnet is moved

2. Increase the number of turns on the coils of wire

3. Increase the strength of the magnetic field

How to reverse the direction of a induced voltage

1. Reverse the connections

2. Reverse the poles of the magnet

Describe the construction of a transformer

- A primary and secondary coil

- Wrapped around a soft iron core.

How and why are transformers used on the national grid?

- Voltage is increased

- Current is decreased

- Which reduces heat loss from high current

- Therefore there is less power loss from heat

- Step down transformer reduces voltage for safety