3. Attraction and repulsion Magnetism is an
example of a non-
contact force. A
force that the
effects are seen
without touching
A permanent
magnetic
produces its
own
magnetic
field
4. 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)
Magnetic induction
5.
6.
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 field
1. Place a plotting compass near the north/south pole of the magnet
and mark the direction that the compass points
2. Move the plotting compass around the bar magnet marking at
regular intervals the direction the compass points
3. Join the points up and add an arrow pointing from the north pole to
the south pole
1
2
3
4
5
6
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. N
S
The magnetic field of a
solenoid is same shape as
that of a bar magnet
Increasing the strength of an electromagnetic
You can increase the strength of
the electromagnetic in 3 ways:
Add more coils
Increase the current
Add an iron core
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.
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?
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)
36.
37.
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.
39.
40.
41.
42.
43.
44.
45. What is a microphone?
• A microphone is a device which
generates electricity from sound waves.
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.
