Download unit62ppt - Macmillan Academy

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
N
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
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
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
Coil of wire
S
More turns of wire
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
2. The coil of wire is in a magnetic field
Reverse the magnetic
field
3. Which makes it turn
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
The dynamo
1. Magnet rotates
N
S
Iron core
Coil of wire
2. Induces a changing
magnetic field in the core
3. The magnetic field
induces an a.c current in
the coil
Spinning the magnet faster increases….
the frequency and the voltage
Increasing the number of turns increases….
the voltage
The A.C. generator
1 The axle is made to turn
2
The coil spins in a
magnetic field
3
A current is induced
Works just like a dc dynamo but……
Each slip ring is connected to a different end of the coil. This
produces……..
An alternating current (a.c)