Science
Physics GCSE
Producing
electricity
There are two types of electric current - direct current (DC) and
alternating current (AC). An electric current can be produced by moving a
magnet inside a coil of wire. The size of this induced current can be increased
by moving the magnet faster, by using a stronger magnet, or by increasing the
number of turns on the coil and increasing its area. A dynamo is a type of
electricity generator.
Direct and alternative current
There are two types of electric current:
·
direct current - DC
·
alternating current - AC
Direct current
Direct current
If the current flows in only one direction it is called direct current,
or DC. Batteries and solar cells supply DC electricity. A typical battery may
supply 1.5V. The diagram shows an oscilloscope screen displaying the signal
from a DC supply.
Alternating current
Alternating current
If the current constantly changes direction it is called alternating
current, or AC. Mains electricity is an AC supply. The UK mains supply is about
230V. It has a frequency of 50Hz (50 hertz), which means that it changes
direction and back again 50 times a second. The diagram shows an oscilloscope
screen displaying the signal from an AC supply.
Making electricity
You should know how to produce an electric current using a coil of wire
and a magnet.
Induction
An electric current is produced when a magnet is moved into a coil of
wire in a circuit. We say that the electric current has been induced, and the
process is called induction. The direction of the induced current is reversed
when the magnet is moved out of the coil again. It can also be reversed if the
other pole of the magnet is moved into the coil. Check your understanding of
this with this simulation.
Notice that no current is induced when the magnet is still, even if it
is inside the coil.
Increasing the induced current
To increase the induced current:
·
move the magnet faster
·
use a stronger magnet
·
increase the number of turns on the coil
·
increase the area of the coil.
Dynamos
It is not practical to generate large amounts of electricity by passing
a magnet in and out of a coil of wire. Instead, generators induce a current by
spinning a coil of wire inside a magnetic field, or by spinning a magnet inside
a coil of wire. As this happens, a potential difference - voltage - is produced
between the ends of the coil, which causes a current to flow.
One simple example of a generator is the bicycle dynamo. The dynamo has
a wheel that touches the back tyre. As the bicycle moves, the wheel turns a
magnet inside a coil. This induces enough electricity to run the bicycle's
lights.
The faster the bicycle moves, the greater the induced current and the
brighter the lights.
Large-scale electricity production
Generators are the devices that transfer kinetic
energy into electrical energy.
Turning generators directly
Generators can be turned directly, for example, by:
·
wind turbines
·
hydroelectric turbines
·
wave and tidal turbines.
When electricity is generated using wave, wind, tidal or hydroelectric
power (HEP) there are two steps:
1.
The turbine turns a generator.
2.
Electricity is produced.
Turning generators indirectly
Generators can be turned indirectly using fossil or nuclear fuels. The
heat from the fuel boils water to make steam, which expands and pushes against
the blades of a turbine. The spinning
turbine then turns the generator.
These are the steps by which electricity is generated from fossil fuels:
1. Heat is released from fuel and boils
the water to make steam.
2. The steam turns the turbine.
3. The turbine turns a generator and
electricity is produced.
4. The electricity goes to the
transformers to produce the correct voltage.
Efficiency of power stations
The energy produced by burning fuel is transferred as heat and stored in
water as steam. The energy in
steam is transferred to movement in a turbine, then to electrical energy in the
turbine. Energy is lost to the environment at each stage.
Here is a Sankey diagram to show these losses.
Sankey diagram
Note that only about a third of the energy stored in the fuel was
transferred as electrical energy to customers.
Different sources of energy
Renewable energy sources
Our renewable energy resources will never run out: their supply is not
limited, and there are no fuel costs either. They typically generate far less
pollution than fossil fuels.
Renewable energy resources include:
·
wind energy
·
water energy, such as wave machines, tidal barrages and hydroelectric
power
·
geothermal energy
·
solar energy
·
biomass energy, for example energy released from wood.
A wind turbine
However, there are somedisadvantages to generating energy from renewable sources: for example, wind farms are
noisy and may spoil the view of people who live near them. The amount of electricity
generated depends on the strength of the wind. If there is no wind, there is no
electricity.
Non-renewable energy sources
There is a limited supply of non-renewable energy resources, which will
eventually run out.
They include:
·
fossil fuels, such as coal, oil and natural gas
·
nuclear fuels, such as uranium.
Fossil fuels release carbon dioxide when they burn, which adds to the greenhouse effect and increases global warming. Of the
three fossil fuels, coal produces the most carbon dioxide, for a given amount
of energy released, while natural gas generates the least.
greenhouse effect: The absorption of heat energy by gases in the atmosphere,
especially carbon dioxide and methane.
The fuel for nuclear power stations is relatively cheap. But the power
stations themselves are expensive to build. It is also very expensive to
dismantle old nuclear power stations or store radioactive waste, which is a
dangerous health hazard.
In an exam question you may be asked to discuss the advantages and disadvantages
of methods of large-scale electricity production. You should list both
renewable and non-renewable resources with advantages and disadvantages for
both.
No comments:
Post a Comment