Download P1 Revision Part 2 File

Methods of Generating
Electricity
Thermal power stations
What does a thermal
power station do ?
A thermal power station
generates electricity by using
the heat produced by the
burning a fossil fuel such as
coal, gas, oil or by the fission
of uranium.
Thermal power station block diagram
Can you draw and explain it ?
BOILER
TURBINES
GENERATOR
BOILER
Fuel is burnt to turn water into high pressure steam.
TURBINE
High pressure steam turns a turbine (like a windmill)
GENERATOR
The turbine rotates the coils of a generator to produce
electricity.
Coal-fired power station
A Nuclear Reactor
Comparison of uranium and fossil fuels
Energy
released per kg
of fuel
Waste
Greenhouse
gases
uranium
coal, gas, oil
1 000 000 kWh
100 kWh
radioactive waste that needs
to be stored for many years
non-radioactive waste
None
Yes, mostly
carbon dioxide
Renewable energy sources
A renewable energy resource is one that will not run
out. It is continually replaced.
Renewable energy sources do not produce radioactive
waste, greenhouse gases or acid rain.
Examples include wind, hydroelectric, wave, tidal, solar
and geothermal.
Fossil fuels such as coal. gas and oil as well as uranium
are non-renewable energy sources.
Wind power
Wind is used to drive a
turbine directly which
rotates an electrical
generator.
A wind farm
Wind power versus thermal power stations
ADVANTAGES
• Renewable energy source
• No greenhouse gases
• No acid rain
• No radioactive waste
• Inexpensive to build
• Short start up time
DISADVANTAGES
• Unreliable – needs wind!
• Best used in places where
they will often be regarded as
unsightly
• Many turbines are needed to
produce the same energy of
a small thermal power
station
• Noise
• Danger to wildlife
Wave power
Waves can be used to
drive an electrical
generator.
Wave power versus thermal power stations
ADVANTAGES
• Renewable
• No greenhouse gases
• No acid rain
• No radioactive waste
• No land needed
• Short start up time
DISADVANTAGES
• Unreliable
• Can only be used in areas
with suitable waves
• Prone to storm damage
• Many needed to produce the
same energy of a small
thermal power station
• Danger to shipping
Hydroelectric power
Falling water is used to
drive a turbine directly
which rotates an electrical
generator.
The Hoover Dam near Las Vegas
Hydroelectric power station
Hydroelectric power versus thermal power
stations
ADVANTAGES
• Renewable
• Can produce as much
energy as a thermal
power station
• No greenhouse gases
• No acid rain
• No radioactive waste
• Short start up time
DISADVANTAGES
• Can only be used in
mountainous areas
• A large amount of land
needs to be flooded
• Expensive to build
• Destroys animal habitats
Tidal power
Moving water caused by the
tides is used to drive a turbine
directly which rotates an
electrical generator.
Proposed Severn Estuary Tidal
Power Scheme
Tidal power station at La
Rance, Brittany
Tidal power station
Tidal power versus thermal power stations
ADVANTAGES
• Renewable
• No greenhouse gases
• No acid rain
• No radioactive waste
• Short start up time
DISADVANTAGES
• Very limited locations
• Wildlife affected
• Expensive to build
Solar power (cells)
Electricity can be
produced directly from
the Sun’s radiation using
solar cells.
Solar power (panels)
Solar panels are used to heat
water saving electricity or
gas use.
Solar power versus thermal power stations
ADVANTAGES
• Renewable
• No greenhouse gases
• No acid rain
• No radioactive waste
• Short start up time
DISADVANTAGES
• Unreliable in the UK! –
sunshine is needed for solar
cells
• Can only be used during the
day
• Only 10% of solar energy is
converted into electricity by
solar cells
• Many cells needed to
produce the same energy of
a small thermal power
station
Geothermal energy
In some volcanic areas hot
water and steam rise to
the surface. The steam
can be tapped and used to
drive turbines. This is
known as geothermal
energy.
Geothermal versus thermal power stations
ADVANTAGES
• Renewable
• No greenhouse gases
• No acid rain
• No radioactive waste
• Short start up time
DISADVANTAGES
• Very limited locations
• Expensive to build
Electricity Generation pie-chart
Most of our electricity is
generated by burning
fossil fuels (74%
according to the pie
chart opposite)
Nearly 20% is nuclear
Less than 5% is currently
generated using
renewable sources.
Problems with fossil fuels
Burning coal, gas and oil produces carbon dioxide.
This is a greenhouse gas which causes global
warming.
Fossil fuel burning can also produce sulfur dioxide
gas. This can dissolve in water and produce acid
rain which causes damage to forests and buildings.
Modern power stations remove most sulfur dioxide
producing compounds before burning.
Fossil fuels are not renewable. They are running
out. Estimates vary between 50 to 200 years to
when we will need to find alternative sources of
energy.
An effect of acid
rain
Problems with nuclear power stations
Nuclear fuel (uranium) does not produce
greenhouse gases and it generates
10000 times more energy per kilogram
than fossil fuels.
However:
Nuclear waste is radioactive and may
have to be stored safely for thousands of
years.
Power stations have to be
decommissioned (dismantle and remove
radioactive waste / materials / fuel )
Although safe in normal operation,
accidents can release radioactive
material over a large area. The area
around Chernobyl in Ukraine has been
closed off since 1986.
The destroyed Chernobyl
nuclear reactor
Pumped Storage Systems
Why do we need pumped storage systems ?
The demand for electricity varies throughout the day, if
there is a sudden increase in demand water flows down
and generates electricity quickly. The water is pumped
back up at night when there is a low demand for electricity.
Pumped Storage Systems
Is there any other way of coping with sudden increases ?
Gas fired power stations have the quickest start up time,
so they can be used to provide extra power above the
base load.
Base Load
The National Grid
What is the National Grid ?
The national
grid is a
system of
cables and
transformers.
The National Grid
Step-Up
Transformer
Step-Down
Transformer
The National Grid
Why do we use transformers ?
By stepping up the voltage ( using the step up
transformer) the current goes down. Low current
means the wires don’t get hot so less energy is
wasted .The voltage is then stepped down ( by the
step down transformer ) to houses so its safer.
The transformers make the system more efficient.
Waves for
Communicating and
understanding the
Universe
Waves
What are longitudinal and transverse waves ?
In a transverse wave the oscillations are perpendicular to the direction of
energy transfer.
In a longitudinal wave the oscillations are parallel to the direction of energy
transfer.
Wavelength of a transverse wave
The wavelength of any wave is the distance between two matching points on
neighbouring waves.
wavelength
wavelength
wavelength
The wavelength is the same whichever two matching points are used to measure this
distance.
The symbol used to represent wavelength is .
Amplitude of a transverse wave
The amplitude of any wave is the maximum distance a point moves from its rest position.
amplitude
amplitude
The amplitude of a transverse wave is the height of a peak or trough from the wave’s
rest position of the wave.
The larger the amplitude, greater the energy of the wave.
Investigating transverse waves
Frequency of transverse waves
The frequency is the number of waves passing any point
each second.
 frequency = number of waves past a point / time
 frequency is measured in hertz (Hz)
 1 wave per second = 1 Hz
 1000 waves per second = 1kHz
 1,000,000 waves per second = 1Mhz
 1,000,000,000 waves per second = 1GHz
What is the formula for wave speed?
For any set of waves, the wave speed (v) can be calculated from the frequency (f) and
wavelength () using this formula:
wave speed = frequency x wavelength
v = f x 
What are the units of speed, frequency and wavelength?
 Wave speed is measured in metres per second (m/s).
 Frequency is measured in hertz (Hz).
 Wavelength is measured in metres (m).
Can I use a formula triangle?
A formula triangle helps you to rearrange a formula.
The formula triangle for wave speed (v), frequency (f)
and wavelength () is shown below.
Cover the quantity that you are trying to work out, which
gives the rearranged formula needed for the calculation.
So to find frequency (f),
cover up f…


x
…which gives
the formula…
f =
v

Wave calculations
A microwave with a frequency of 2.4GHz travels
at 3 x 108 m/s . What is its wavelength?
2.4 GHz = 2,400,000,000 Hz or 2.4 x 109 Hz
wavelength = speed / frequency
wavelength = 3 x 10 8 / 2.4 x 109 = 0.125 m
Be careful with units – wavelength is in meters
Electromagnetic waves are transverse
As the wavelength of EM spectrum changes, the way the different
wavelengths interact with matter also changes.
As the frequency increases, wavelength gets smaller. Eventually the
waves are so small that they can interact with cells, DNA and atoms. This
is called IONISING RADIATION.
NON-IONISING
IONISING
Uses of EM Waves
Wave
Uses
Radio waves
Television and radio transmission
Microwaves
Mobile phones , cooking and
satellite communication
Infra red
Thermal imaging, cooking,
optical fibres , security systems
TV Remote Control
Visible light
Vision, Photography
Ultraviolet
Detecting forged banknotes
tanning, disinfecting water
X-rays
Medical images of bones
Gamma rays
Killing cancer cells , sterilising
food and medical equipment
Harmful Effects of EM Waves
Wave
Uses
Microwaves
Internal Heating of Body Cells
Infra red
Skin Burns
Ultraviolet
Skin cancer and Cataracts
X-rays
Mutation & damage to cells
Gamma rays
Mutation & damage to cells
Reflection
Can you draw what happens to light when it is
reflected by a mirror ?
The angle of incidence is equal to the angle of reflection
The normal is at 90O to the mirror
Your diagram must have arrows on the rays.
Reflection
Can you draw how an image is formed in a plane
mirror ?
The image is the same distance behind as the object is in front
The image is virtual ( its formed by those dotted lines)
Diffraction
What is diffraction ?
The spreading out of waves as they pass through a gap or
around an object. Most diffraction when the gap is about
the same size as the wavelength of the wave.
Sound
What type of wave is a sound wave ?
It is a longitudinal wave made up of squashes ( compressions)
and stretches ( rarefactions)
Sound
What happens when a sound wave hits an object ?
It is reflected – we call this an echo.
Red Shift
What does this diagram show?
When a source of waves moves towards us the waves are squashed ( wavelength
smaller , frequency higher)
When a source of waves away from us the waves are stretched ( wavelength
bigger , frequency lower)
Red Shift
Why is the Doppler effect important?
We observe that light from distant galaxies is shifted towards
the red part of the spectrum – this must mean that they are
moving away from us. The universe is expanding !.This also
means that at some point in the past they must have been
closer.
( Light from distant galaxies does not look redder)
Red Shift
What is special about the expansion of the
universe?
The further a galaxy is from earth the bigger its red shift .
This gives the examiner a chance to ask about distance and
speed being directly proportional.
The Big Bang Theory
What is the Big Bang Theory?
The theory that the universe started as a tiny hot mass where
all the matter in the universe was concentrated.
The main evidence to support this theory comes from:
Red shift and
The Cosmic microwave background radiation.
Remember that scientists cannot say what happened before
the big bang because there is no evidence.
The Big Bang Theory
What is the cosmic microwave background
radiation?
This is microwave radiation that fills the universe wherever
you look. It comes from radiation produced by the big bang.