2. Magnetic or non-magnetic?

3. What is a magnetic field?
The region around a magnet where it has a magnetic effect is called its magnetic field.
When a magnetic material is placed in a magnetic field it will experience a force.
The iron filings feel the effect of the magnetic field and line up along the direction of the forces in this region.
magnetic field

4. weakest field further away from poles
Magnetic field lines
The shape of a magnetic field can be shown by drawing magnetic field lines. These always point from the north pole of a magnet to the south pole, along the direction of the magnetic forces in each region. Where is the magnetic field strongest?
strongest field at
poles
The closer together the magnetic field lines, the stronger the magnetic field.
weakest field further away from poles

5. Forces between magnets experiment

6. The Earth’s magnetic field
People have used magnetism to navigate for hundreds of years. The Earth’s iron core creates a magnetic field. The north poles of magnets, such as compass needles, are attracted to the North Pole of the Earth.
But if like poles repel, why is the north pole of a magnet attracted to the North Pole of the Earth?
These poles were named before magnetism was properly understood. The ‘Magnetic North Pole’ of the Earth is really a magnetic south pole.
Do you think that you would be able to use a compass to navigate on other planets, or on the moon?

7. Making an electromagnet

8. Investigating electromagnets
The strength of an electromagnet depends on whether it has a core of iron.
Two experiments can be carried out to investigate the other factors that can affect the strength of an electromagnet:
Investigate how the number of coils affects the number of drawing pins attracted to an electromagnet – keep the current the same in this experiment.
Investigate how the size of the current affects the number of drawing pins attracted to an electromagnet – keep the number of coils the same in this experiment.

9. Investigating electromagnets – results
Here are some example results. 8 18 31 46 20 40 60 80
number of coils
number of drawing pins attracted 12 23 38 49 1 2 3 4
current (A)
number of drawing pins attracted

10. Investigating electromagnets – analysis
How did the number of coils affect the number of drawing pins attracted to the electromagnet? 50 40 30 20 10 60 80
100
number of coils
number of drawing pins attracted

11. Investigating electromagnets – analysis
How did the size of the current affect the number of drawing pins attracted to the electromagnet? 60 40 30 20 10 1 2 3 4 5
current (A)
number of drawing pins attracted 50

12. Using electromagnets – recycling
A large electromagnet is used on a recycling plant conveyor belt to pick up and move metal cans.
Which metals would the electromagnet attract?
What advantages does an electromagnet have over a permanent magnet?

13. Uses of electromagnets – electric bell
The circuit for a door bell includes an electromagnet.
When the circuit is closed, the electromagnet pulls the armature towards it, causing the hammer to strike the bell.
The movement of the armature breaks the circuit, and the hammer returns to its original position.
This sequence repeats, causing the bell to sound continuously.
Worksheet 3 accompanies this slide.

14. Now Read pages 270-272 from your Textbook
Extra Task:
Now Read pages from your Textbook