AC

1
AC DC Generators
LEARNING OUTCOMES Recognise the differences
between DC and AC and illustrate them
diagrammatically Describe how simple generators
work using the dynamo effect .
2
DC DIRECT CURRENT The current flows in one
direction, from to -. Eg, a battery AC
ALTERNATING CURRENT The current keeps reversing
direction, since the 2 terminals alternately
become and Eg, mains electricity (in the UK
it alternates 50 times per second, so frequency
50Hz). If we know how long 1 wave lasts for (the
period) then the inverse is the frequency. Eg,
waves lasts for 0.1s, so the frequency is 1 / 0.1
10Hz.
3
Electromagnetic Induction
The field lines have to be cut. No current is
produced if the magnet is not moving!
N
If You push a magnet into a coil the electrons in
the coil are also given a push. This makes an
induced voltage
4
Electromagnetic Induction
Notice the needle moves in the opposite direction
N
If You pull a magnet out of the coil the
electrons in the coil are once again given a
push. This makes an induced voltage in the
opposite direction
5
How Can You Increase the Size of the Induced
Current?

1. Move the Magnet Faster
2. Use a Stronger (not bigger!) Magnet
3. Put more Turns on the Coil

6
We can use a magnet, coil and movement to
generate electricity with this device
Will it make AC or DC Current?
7
This is a Generator
You will have heard them near road works
generating the electricity to make the traffic
lights and machines work
8
AC Generator

• Induced current can be increased in 4 ways
• Increasing the speed of movement
• Increasing the magnetic field strength
• Increasing the number of turns on the coil
• Increasing the area of the coil

9
Bikes often have Dynamos to make electricity to
light a bulb
Dynamos are slightly different from generators as
they rotate the magnet
10
Power stations Efficiency
LEARNING OUTCOMES Describe how the dynamo
effect is used in conventional power stations to
generate electricity burning fuel producing
steam spinning a turbine turbine turns
generator. Be able to use equations to calculate
efficiency in a variety of situations. Describe
recognise that there is significant waste of
energy in a conventional power station.
11
(No Transcript)
12
(No Transcript)
13
Transformers
LEARNING OUTCOMES Explain how transformers are
used on the National grid to transmit electricity
at high voltage to reduce energy
waste/costs. Explain how, for a given power,
increased voltage reduces current. This will
decrease energy waste by reducing heating of
cables.
14
(No Transcript)