Unit 6 in four lessons

1
Unit 6 in four lessons
Electro - magnetism
2
The link between electricity magnetism
When a wire moves through a magnetic field a
voltage is produced
N
S
Moving a magnet moves through a coil of wire will
induce a current
Moving the magnet faster increases the
current. Moving the magnet out makes the magnet
go in the opposite direction Putting the south
pole first also changes the directions of the
current
N
3
Currents and magnetic fields
All currents produce a magnetic field
The magnetic field along a current in a wire
looks like..
A series of circles running perpendicular to the
wire
The magnetic field around a coil or solenoid
looks like..
The shape of a bar magnets field
Iron core
Coil of wire
4
If a wire with a current flowing goes through a
magnetic field it is forced to move (up or
down). If you coil a wire it will rotate. This is
how motors work
How can you make it turn faster?
N
Larger current Stronger magnets More turns of wire
Coil of wire
S
Commutator Keeps the motor turning in the same
direction
How can you make it turn the other way?
1. A current goes through the wire
Reverse the current Reverse the magnetic field
2. The coil of wire is in a magnetic field
3. Which makes it turn
5
To improve the efficiency of commercial motors
the coil is cylindrical
The motor only turns efficiently if the coil is
90 degrees to the magnetic field
If the magnets have curved faces and the coil is
also cylindrical then it will always be 90
degrees to the magnet We say it has a radial field
6
The dynamo

1. Magnet rotates

2. Induces a changing magnetic field in the core
N S
Iron core
3. The magnetic field induces an a.c current in
the coil
Coil of wire
Spinning the magnet faster increases.
the frequency and the voltage
Increasing the number of turns increases.
the voltage
7
The A.C. generator
1
The axle is made to turn
2
The coil spins in a magnetic field
3
A current is induced
Each slip ring is connected to a different end of
the coil. This produces..
An alternating current (a.c)