Transcript Energy & Electricity

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 .
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.
Electromagnetic Induction
N
The ‘field
lines’ have
to be cut.
No current
is produced
if the
magnet is
not moving!
If You push a magnet into a coil the
electrons in the coil are also given a
push. This makes an ‘induced voltage’
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
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
We can use a magnet, coil and
movement to generate electricity
with this device
Will it make AC or DC Current?
This is a Generator
You will have heard them near road
works generating the electricity to
make the traffic lights and
machines work
AC Generator
Induced current can be increased
in 4 ways:
1) Increasing the speed of movement
2) Increasing the magnetic field strength
3) Increasing the number of turns on the
coil
4) Increasing the area of the coil
Bikes often have Dynamos to make
electricity to light a bulb
Dynamos are slightly
different from
generators as they
rotate the magnet
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.
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.