3. Attraction and repulsion
A permanent magnetic produces its own magnetic field
Magnetism is an example of a non-contact force. A force that the effects are seen without touching

4. Magnetic induction Magnetism can be induced in magnetic materials by:
Placing them in a magnetic field.
Stroking them with another magnet.
Induced magnetism always causes a force of attraction
Magnetic materials can be hard or soft:
Magnetically soft materials gain and lose their magnetism easily. (e.g iron)
Magnetically hard materials are harder to magnetise, but they retain their magnetism. (e.g steel)

7. Magnetic field lines Field Line Rules:
Magnetic field lines of force show:
the shape of the magnetic field.
the direction of the field lines – north to south.
the strength of the magnetic field. closer together = stronger.

8. How to plot a magnetic field5 1 2 6 3
Place a plotting compass near the north/south pole of the magnet and mark the direction that the compass points
Move the plotting compass around the bar magnet marking at regular intervals the direction the compass points
Join the points up and add an arrow pointing from the north pole to the south pole 4

12. Magnetic field around a conductor
Current Carrying Wires:
A current carrying wire will create a magnetic field around it

13. Magnetic field around a conductor

14. Increasing the strength
Electromagnets are made stronger by coiling the wire
A wire that is coiled into a spiral is known as a solenoid

15. Increasing the strength of an electromagnetic
The magnetic field of a solenoid is same shape as that of a bar magnet
You can increase the strength of the electromagnetic in 3 ways:
Add more coils
Increase the current
Add an iron core
N S

16. Increasing the strength
aNticlockwise = North
clockwiSe = South

18. Uses of electromagnets – scrapyard crane & circuit breaker

19. Uses of electromagnets – electric bell

20. Uses of electromagnets – the relay

23. Magnetic Force
A current carrying wire has a magnetic field around it. If it is placed at right angles to another magnetic field, it will experience a force.

24. Fleming’s left hand Rule
We can use Fleming’s left hand rule to tell us the direction of the force on a current carrying conductor.

25. Fleming’s left hand Rule

26. Example
FORCE S N
MAGNETIC
FORCE
CURRENT

29. Turning effect on a coilS

30. How does an electric motor works?
We’ve seen how the wire will turn when current is passed through it, how can we use this to make an electric motor?

31. DC(Direct Current) Electric motor

32. Commutator
Commutator
The commutator is what allows the motor to keep turning.
Without this it would just stay in one position - - + +

33. Commutator
As the coil turns the commuator ensures that the coil keeps turning by switching the current from positive to negative

34. Overall – Which way is the current travelling?

35. How to make more turning effect
The turning effect on a coil can be increase by;
Increasing the current
Using a stronger magnet
Increasing the number of turns on the coil
Increasing the area of the coil – wider (more leverage) or longer (more magnetic field generated)

38. How does a speaker work?
The signal source causes current to flow through the coil and creates an electromagnet. ↓
The size of the current varies depending on the electric signal and so the strength of the electromagnet varies.
The permanent magnet is attracted or repelled by the electromagnet.
The movement of the permanent magnet causes the cup to vibrate.
The vibrating cup pressurises the surrounding air producing sound waves.

45. What is a microphone?
A microphone is a device which generates electricity from sound waves.

46. How does a microphone work?

47. How does a microphone work?
The person speaks, creating sound waves ↓
The sound waves strike the diaphragm and move it backwards and forwards at the same frequency as the sound
The moving diaphragm moves the coil backwards and forwards which induces a changing current at the same frequency as the sound.
This changing current (called the signal) can be used for recording or the signal can be sent to an amplifier which makes the signal big enough to drive loudspeakers.
The loudspeaker converts the signal back into the original sound.