Transcript P1b_Revision_lesson

OCR 21st Century Science
Unit P1a Revision
The earth in the universe
The eight planets of our Solar System
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Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
As well as the eight planets, the solar system is also made
up of asteroids, dwarf planets, comets and moons
Different Orbits
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Mercury = 88 days
Mercury
Venus
Earth
Mars
Mars = 687 days
Pluto =
Jupiter
90,500 days
Saturn
Uranus
Neptune
Pluto
Asteroids
An “asteroid belt” lies between Mars and
Jupiter. But what is an asteroid?
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Comets
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Comets are balls of dust and frozen
gas. They have very elliptical orbits:
Notice how the tail always points away from the sun!
The Solar System summarised
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What makes up our solar system? Complete the following mind
map with what you now about each object:
The solar system
Solar systems, galaxies and the Universe
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Our planet (around 13,000km diameter and 4500 million
years old) is pretty small compared to...
OUR SUN (100 times wider
and 4.6 billion years old),
which is small compared to…
THE UNIVERSE, which
contains billions of galaxies and
is 14,000 million years old.
THE MILKY WAY, which
contains at least 200 billion
stars and is 100,000 light
years across, which is small
compared to…
How to make a solar system
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……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
…………………………………………………………………………………………………
Stage 1: Nebulae
A nebulae is a collection of dust, gas and rock.
Some examples of nebulae…
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Stage 2: Throw the nebula together
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Gravity will slowly pull these
particles together…
As they move inwards their
gravitational potential energy
is converted into heat and a
big object (PROTOSTAR) or
smaller objects (planets,
asteroids etc) are formed
Stage 3: Make a star
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In a star the forces of
gravitational attraction
pulling the particles inwards
are _________ by forces
acting outwards due to the
huge __________ inside the
star.
Stars are basically ________ reactors that use _______
as a fuel. During its main sequence a star will release
energy by combining hydrogen and helium nuclei (light
elements) into _________ elements.
Any element in space that is heavier than helium is
thought to have been made in a star.
Words – heavier, balanced, hydrogen, nuclear, temperatures
Observing the Universe
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All of these methods rely on detecting radiation from stars.
The Light Year
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Distances in space are so big that they are measured in units
called “light years”:
1 light year = the distance
travelled by light in one yar
Q. If light travels through space (i.e. A vacuum) at 300,000
km/s how far is one light year?
Because of this, when we see stars in the night sky we are
actually seeing them as they were in the past.
Distances in space
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The Sun, our closest star, is 1.6x10-5 light years
away from us.
The next closest star, Proxima
Centauri (4.2 light years away)
The centre of our galaxy, the Milky Way, is
around 26,000 light years away.
The Andromeda Galaxy (our closest galaxy)
– approximately 2.5 million light years away
Measuring distance using brightness
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When I look at these stars some appear brighter than
others. This because they are either brighter stars or
closer to me.
For example, the star Antares is 10,000 times brighter
than the sun but it is 500 light years away from me, so it
is only the 15th brightest star in the night sky.
Measuring distances to stars
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1) Relative Brightness
The further away a
star is the dimmer it
is. Simple.
2) Parallax
Parallax is the
apparent change in
position of closer
stars due to the
Earth moving around
the sun.
Distant
stars
Nearby star
Problems in Measuring Distances
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1) Light pollution and other
atmospheric conditions can
interfere with observing stars:
2) Stars are simply very far away so the
angles involved in using techniques like
parallax are very small:
How our Earth and the Sun
compare to others…
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How did the universe begin?
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Scientists believe that the universe began by a “big bang”
around 14 billion years ago:
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Evidence about the origins of
the universe…
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Source of
light
“Spectra”
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If you pass the light through a gas something
different is seen…
helium
Some wavelengths of light
are absorbed by the gas –
an “absorption spectrum”.
If the light source is moving away the absorption
spectra look a little different…
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Before
helium
helium
After
The absorption lines have all been “shifted”
towards the longer wavelength end (red end)…
This is called red
shift. The faster
the light source
moves the further
its light will be
“shifted”
Before
After
A similar effect happens with sound –
this is called “The Doppler Effect”
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Red Shift simplified
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Basically, if I walk towards you I’ll look
slightly more blue. Then, if I walk away
from you, I’ll look slightly more red!!
Let’s try it…
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Light from different stars and from the edge
of the universe also shows this “red-shift”.
This suggests that everything in the universe
is moving away from a single point.
This is the BIG
BANG theory
Red shift summary
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Light from other galaxies has a longer _________ than
expected. This shows that these galaxies are moving ____
from us very quickly. This effect is seen to a greater
extent in galaxies that are _______ away from us. This
indicates that the further away the galaxy is, the ______
it is moving.
This evidence seems to suggest that everything in the
universe is moving away from a single point, and that this
process started around 15 _____ years ago. This is the
____ ________ Theory.
Words to use – faster, away, big bang,
billion, wavelength, further
Hubble’s Law
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The speed at which galaxies are
moving away from us is proportional
to their distance from us.
In other words, the further away
they are, the faster they go.
Edwin Hubble
1889-1953
Big Bang Theory
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Some scientists have explained that red shift can actually be used to
support the Big Bang Theory – this explanation is based around the rates
of expansion and contraction of different galaxies. If our neighbouring
galaxy is expanding at a different rate to the Milky Way then it will appear
red or blue-shifted.
So Mr President, red shift
shows us that galaxies are
moving and therefore we
assume that space itself is
expanding. Elementary!
Stephen Hawking, 1942 -
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The end of the Universe
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There are some theories about how the
universe will end but its difficult to tell due
to difficulties in measuring objects that are
so far away:
“The big crunch” – if there is too much mass (i.e. too much
matter) the universe will collapse under its own gravity. It
may then do another “big bang” – this is the “oscillating
universe” theory.
“Expanding Universe” – if there isn’t enough mass in the
universe then it will just keep on expending forever.
If there is just the right mass in the universe then it will
reach a fixed size.
The End of the Universe
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Basically, how the universe will end
depends on its “energy-mass density”.
Size of universe
Stephen Hawking
Now
Open universe
Critical
density
Closed
universe
Time
OCR 21st Century Science
Unit P1b Revision
The changing earth
Evidence for the age of the Earth
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Scientists once thought that the Earth was only 6000 years
old. Rocks have provided lots of evidence for the world being
older.
1) Erosion
2) Craters
3) Mountains
4) Fossils
5) Folding
6) Radioactive dating
The Earth’s age must be older than the oldest rocks, which are
around 4,000,000,000 years old.
Continental Drift
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Look at the coastlines of South
America and Africa. I wonder of they
used to fit together…
Alfred
Wegener
I’m going to call this my
Theory of Continental Drift
Tectonic theory
What’s my evidence for this? Three things:
1) The “jigsaw fit”
2) Each continent has similar rocks and fossils
3) Each continent has similar animal species
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Another Example of Continental Drift
The formation of mountain ranges can be explained by tectonic
theory. Consider the Himalayas at the top of India:
This is where
India is now
This is where
India was millions
of years ago
If it wasn’t for processes like this then, if you think
about it, continents would eventually disappear due to
erosion. Fascinating.
The Evidence:
Tectonic theory
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1) Some continents look like they used to “fit”
together
2) Similar rock patterns and fossil records
The Problems:
Wegener couldn't explain how continental drift
happened or provide evidence so nobody
believed him. Also, he wasn’t a geologist so he
had no credibility and there were other
explanations for the same evidence.
The Answer:
Scientists discovered 50 years later that the Earth generates massive
amounts of heat through radioactive decay in the core. This heat
generated convection currents in the mantle causing the crust to move.
Conclusion – scientists now believe Wegener’s Tectonic Theory
Movement of the Lithosphere
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The Earth’s LITHOSPHERE (i.e. the _______) is split
up into different sections called ________ plates:
These plates are moving ______ from each other a few
centimetres every _______. They can slide past each
other, move apart from each other or move towards
each other, causing volcanoes and _________.
Words – earthquakes, crust, apart, tectonic, year
Sea Floor Spreading
Earthquakes and
volcanic eruptions can
be common here
Igneous Rock
Oceanic Crust
Mantle
Convection
Currents
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Magma
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Magnetic Patterns in Sea Floor Spreading
The Earth’s magnetic field swaps poles every million years.
The above picture shows those changes recorded over time in
rocks on the sea floor and provides evidence for long-term sea
floor spreading.
More on Plate Movements
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Subduction
Thin, dense oceanic plate
Convection
Currents
Thick, less dense
continental plate
The Structure of the Earth
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A thin crust - 10100km thick and
not very dense
A mantle – extends
almost halfway to the
centre, hot and dense
A core – made of molten
nickel and iron. Outer
part is liquid and inner
part is solid. Gets hot
due to radioactive decay.
How do we know? A lot of the evidence for these facts
comes from studying earthquakes (seismic waves)…
An introduction to Waves
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A Wave is a “movement of energy” but NOT a transfer of
matter
Transverse vs. longitudinal waves
Transverse waves
are when the
displacement is at
right angles to the
direction of the
wave.
Displacement
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Direction
Examples – light, other EM waves, some seismic waves
Displacement
Direction
Longitudinal waves
are when the
displacement is
parallel to the
direction of the
wave…
Examples – sound, some seismic waves
Seismic waves
Earthquakes travel as waves through the Earth – we call them
SEISMIC WAVES. There are two types:
P waves:
1) They are longitudinal so they cause the ground
to move up and down
2) They can pass through solids and liquids
3) They go faster through more dense material
S waves:
1) They are transverse so they cause the ground
to move from right to left
2) They ONLY pass through solids
3) They are slower than P waves
4) They go faster through more dense material
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Seismic waves
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These P waves are
being reflected at the
crust
These P waves travel
through the Earth and
are refracted when
they pass through a
medium
The paths of these waves are all
curved because density is
gradually changing
These S waves cannot
travel through the
outer core as they only
go through solids – this
tells us that the outer
core is liquid
Locating Earthquakes
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By measuring the time
it takes the wave to
travel to these
locations the location
of the earthquake can
be found.
Wave definitions…
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1) Amplitude – this is
“how high” the wave
is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
4) Speed – this is how fast the wave travels and is
measured in metres per second (m/s)
Distance, Speed
and Time for waves
Speed = distance (in metres)
time (in seconds)
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D
S
T
1) A water wave travels 200 metres in 40 seconds. What is its speed?
2) Another wave covers 2km in 1,000 seconds. What is its speed?
3) Sound travels at around 330m/s. How long does it take to travel one
mile (roughly 1,600m)?
4) Light travels at a speed of 300,000,000m/s. How long would it take to
travel around the world if the diameter at the equator is around
40,000km?
Drawing waves
1) Low amplitude, low frequency:
2) Low amplitude, high frequency:
3) High amplitude, low frequency:
4) High amplitude, high frequency:
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The Wave Equation
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All E-M waves obey the Wave Equation:
Wave speed (v) = frequency (f) x wavelength ()
in m/s
in Hz
Notice that frequency is
inversely proportional to
wavelength – if wavelength
goes up, frequency goes down
V
f
in m

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Some example wave equation questions
1) A water wave has a frequency of 2Hz and a wavelength
of 0.3m. How fast is it moving?
0.6m/s
2) A water wave travels through a pond with a speed of
1m/s and a frequency of 5Hz. What is the wavelength
of the waves?
0.2m
3) The speed of sound is 330m/s (in air). When Dave
hears this sound his ear vibrates 660 times a second.
What was the wavelength of the sound?
0.5m
4) Purple light has a wavelength of around 6x10-7m and a
frequency of 5x1014Hz. What is the speed of purple
light?
3x108m/s
OCR 21st Century Science
Unit P2a Revision
Electromagnetic radiation
Radiation – the basics
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Lots of objects (“sources”) emit radiation. For example,
consider the sun. The sun, amongst others, emits light and
heat:
Wow it’s hot here!
I’m not so
bad thanks
When radiation hits a surface it is usually either
absorbed, reflected or transmitted, or a combination of
these things.
Light
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White light is a mixture of colours:
RED LIGHT is made
of “low energy
photons”
PURPLE LIGHT is made
of “high energy photons”
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The Electromagnetic Spectrum
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Each type of radiation shown in the electromagnetic spectrum has a
different wavelength and a different frequency:
High frequency,
____ energy
Gamma
rays
X-rays
Low frequency,
________ energy
Ultra violet
Visible
light
Infra red
Microwaves
Radio/TV
γ
Each of these types travels at the same speed through a _______
(300,000km/s), and different wavelengths are absorbed by different
surfaces (e.g. infra red is absorbed very well by ___________ surfaces).
This absorption may heat the material up (like infra red and _______) or
cause an alternating current (like in a __ _______).
Words – black, microwaves, low, high, TV aerial, vacuum
Photons
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Light (and the other types of EM radiation) travel in “packets”
called photons:
Here comes a photon…
And another…
And another…
Higher frequency radiation (i.e.
gamma and x rays) consist of
photons of higher energy.
Intensity of light and heat
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The heat here is
very intense!
The heat
here isn’t so
bad... Why?
When a body absorbs radiation the amount of heat it
gains depends on the intensity (power per square metre
per second) and the time of the exposure.
An example question
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Which of these surfaces would warm up the quickest when
receiving infra red photons from the sun?
What factors are affecting the answer?
Intensity
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Clearly, the intensity of radiation received by an object
decreases the further out the object is. This is due to two
things:
1) The radiation “spreads out” in a circle
2) It is also absorbed by the medium it travels through
Ionisation
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Some types of radiation are dangerous because they “ionise” atoms – in
other words, they change atoms by turning them into _____ by “knocking
off” __________:
Ionisation causes chemical reactions which cause _____ in living tissue to
mutate, usually causing _______. High doses can destroy cells completely,
causing radiation sickness. This takes a lot of ______ so only high energy
radiations like ________, x rays and ultra violet can do it.
Words – energy, gamma, electrons, ions, cancer, cells
Recap on absorbing radiation
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Who would warm up the quickest when receiving infra red
photons from the sun?
What would happen of either of these
people absorbed too much heat?
Dangers of Mobile Phones
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Many people are concerned with the possible
dangers of using mobile phones, especially for
children.
Your task:
Find out about some of the research that has taken place in
the last 20 years over the use of mobile phones, including:
1) Some evidence that using them is dangerous
2) Other evidence that it isn’t
3) Whether or not living near mobile phone masts is dangerous
4) How coming to an overall conclusion can be difficult
How do Microwaves heat food?
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How does the design of a microwave oven protect the user
from harm?
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Introduction to Radioactivity
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Some substances are classed as “radioactive” – this means that
they are unstable and continuously give out radiation:
Radiation
The nucleus is more stable after emitting some gamma
radiation – this is called “radioactive decay”. Increased
exposure to gamma radiation can cause cancer or cell death.
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Warning the Public about UV Dangers
Over the last few years the public has received many warnings
about the dangers of ultraviolet radiation:
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Ozone
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Ozone is a chemical (O3) in the atmosphere that absorbs
harmful UV rays from the sun. This causes chemical reactions
in the atmosphere. Unfortunately, it’s getting thinner:
Diagram showing the quantity
of ozone in different parts of
the southern hemisphere
Global production of CFCs
over the last 60 years –
notice the change!
Suncream
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Ultra violet radiation in sunshine can be dangerous and cause
skin cancer, cataracts and premature skin aging.
It is recommended that you spend no more than 20
minutes in the sun on a sunny day. However, you
could also use suncream:
Of course, wearing clothes always helps!
Protection against harmful radiation
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Physical barriers can be used to absorb radiation, e.g.
A lead screen
protecting from x-rays
The fact that x-rays are
absorbed by hard substances
makes them very useful:
Containment structures around a
nuclear reactor
OCR 21st Century Science
Unit P2b Revision
EM radiation 2
Principal Frequency
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All objects emit radiation of some kind. The “principle
frequency” of that radiation depends on the object’s
temperature. For example, consider a Bunsen burner:
Blue is a higher frequency than yellow light – objects that
are “blue hot” are often hotter than “yellow hot”
The Greenhouse Effect
We get heat
from the sun:
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A lot of this heat is
_______ back into space.
However, most of it is kept
inside the Earth by a layer of
gases (e.g. carbon dioxide and
______) that prevent the heat
escaping by _______ and then
re-radiating it back again.
The Earth reflects back radiation with a lower principal
_______ that the radiation it receives from the sun. This
radiation basically causes the earth to warm up – this is called
“_______ ________” or the “Greenhouse Effect”.
Words – methane, global warming, reflected, absorbing, frequency
Global Warming
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Carbon dioxide, methane and water vapour are all greenhouse gases but
they are only present in small amounts. However, recently this balance has
been getting “upset” causing this:
Facts:
1) The 10 warmest years
of the last century
have all occurred
within the last 15
years
2) Sea level has risen by
between 12 and 24cm
in the last 100 years
3) Rainfall has risen by
1%
Global Warming Predictions
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Data taken from http://en.wikipedia.org/wiki/File:Global_Warming_Predictions.png
The Effects of Global Warming
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The following things could happen as a result of global warming:
1) Food – it will be impossible to
grow crops in particular regions
2) More extreme weather conditions
due to increased convection and larger
amounts of water vapour
3) Flooding of low-lying land
caused by ice caps melting
and expansion of water
The Carbon Cycle
CO2 in air
5. Burning
fossil fuels
also releases
CO2
4. Animals
release CO2
through
respiration
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2. Plants and algae
release CO2 through
respiration
1. CO2 is taken in
by plants and
algae for
photosynthesis
and turned into
carbohydrates,
fats and proteins
3. The carbon taken in
by plants is then eaten
by animals and the
animals that eat them
The Carbon Dioxide Balance
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Carbon dioxide levels in the atmosphere have remained
balanced due to the carbon cycle. However, over the last 200
years the level of CO2 in the atmosphere has risen due to
activities like:
1) Deforestation, which takes away
some of the trees that remove carbon
dioxide
2) Burning fossil fuels, which releases more carbon
into the atmosphere that was previously “locked up”
Reflecting Radio waves
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Some radio waves are refracted and then reflected off the
atmosphere and suffer little absorption, which is useful as
they can travel further distances.
Using Satellites with microwaves
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Microwaves are used
to communicate with
satellites as they are
not absorbed by the
atmosphere
Analogue vs. Digital
Analogue signals (like talking or
music) continually vary in
amplitude and/or frequency
1
0
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+
Digital signals, however, are either
off or on, and the information is sent
in a series of pulses
There are two main advantages of digital:
1) More channels can be sent down the same cable – “multiplexing”
2) Better quality, because a digital signal can be amplified without
amplifying the extra noise:
Transmitting information
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EM waves can also be used as “carrier waves” in order to send a signal:
Signal
Carrier wave
Modulated wave Transmitter
Light signals can also
be sent down optical
fibres where they
travel for long
distances with little
absorption:
Wave is
demodulated
(“decoded”) back
into a signal
Using Light to send Signals
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Morse code is a signal that consists of
short bursts and long bursts and
therefore is classed as a “digital”
signal as each message can be one of
only two forms. These signals could be
relayed between ships over long
distances.
Modern signals can be sent by radio or electric signals
instead. What are the advantages of these methods over
using light?
Storing Digital Signals
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One of the advantages of digital signals is that they can be
stored and processed easily by computers.
Data is measured in units called “bytes”. 1 Byte = 8
bits, and is roughly the amount of data needed to
store one character of text.
Clearly, the large a file size, the more bytes it contains and
therefore the higher quality the sound or image is.
OCR 21st Century Science
Unit P3a Revision
Sustainable energy
Energy Consumption
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The demand for energy is predicted to rise by a large amount
in the next few decades:
What issues will this rise in demand cause?
Fuels
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A “fuel” is something that can be burned to release heat and
light energy. The main examples are:
Coal, oil and gas are called “fossil fuels”. In
other words, they were made from fossils.
Some definitions…
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A renewable energy source is clearly one that can be _______
(“renew = make again”), e.g. _____, solar power, biogas etc.
A ___________ energy source is one that when it has been
used it is gone forever. The main examples are ____, oil and
gas (which are called ______ ____, as they are made from
fossils), and nuclear fuel, which is non-renewable but NOT a
fossil fuel.
Electricity is called a “________ source” because it is
converted from other forms – what would these forms be in
batteries, wind turbines and solar panels?
Words – non-renewable, coal, fossil
fuels, wood, renewed, secondary
Pollution
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When a fuel is burned the two main waste products are _____
dioxide and ________ dioxide.
Carbon dioxide is a _________ ___ and helps cause _______
_________. This is produced when any fossil fuels are
burned.
Sulphur dioxide, when dissolved in ________, causes ______
_____. This is mainly a problem for ___ power stations.
Nuclear power stations do not produce these pollutants
because they don’t ____ fossil fuels.
Words – sulphur, coal, global warming, carbon,
acid rain, greenhouse gas, rainwater, burn
Using Electricity
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Basically, electrical devices are used to transfer electrical
energy to the environment:
+
-
This light bulb will transfer
light and heat to the
surroundings.
Energy and Power
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The POWER RATING of an appliance is simply how much
energy it uses every second.
In other words, 1 Watt = 1 Joule per second
E
E = Energy (in joules)
P = Power (in watts)
T = Time (in seconds)
P
T
Some example questions
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1) What is the power rating of a light bulb that transfers
120 joules of energy in 2 seconds?
60W
2) What is the power of an electric fire that transfers
10,000J of energy in 5 seconds?
2KW
3) Rob runs up the stairs in 5 seconds. If he transfers
1,000,000J of energy in this time what is his power
rating?
0.2MW
4) How much energy does a 150W light bulb transfer in a)
one second, b) one minute?
150J,
9KJ
5) Jonny’s brain needs energy supplied to it at a rate of
40W. How much energy does it need during a 50 minute
physics lesson?
120KJ
6) Lloyd’s brain, being more intelligent, only needs energy at
a rate of about 20W. How much energy would his brain
use in a normal day?
630MJ
Power
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Power is “the rate of doing work”.
The amount of power being used in
an electrical circuit is given by:
Power = voltage x current
in W
in V
in A
P
V
I
We can use this equation to analyse power stations:
1) A transformer gives out 10A at a voltage of 50V. What is
its power output?
500W
2) An electric fire has a power rating of 2KW. If it runs on a
voltage of 230V what is the current?
8.7A
3) Electricity is transmitted along some lines in the National
Grid at 400KV. If the current is 1KA what would be the
power through the wire?
400MW
The Cost of Electricity
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Electricity is measured in units called “kilowatt hours” (kWh).
The kilowatt hour is a unit of energy but the Joule is too small
to count so we use the KWh instead. For example…
A 3kW fire left on for 1 hour uses 3kWh of energy
A 1kW toaster left on for 2 hours uses 2kWh
A 0.5kW hoover left on for 4 hours uses __kWh
A 200W TV left on for 5 hours uses __kWh
A 2kW kettle left on for 15 minutes uses __kWh
The Cost of Electricity
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To work out how much a device costs we do the following:
Cost of electricity = Power (kW) x time (h) x cost per kWh (p)
For example, if electricity costs 8p per unit calculate the cost
of the following…
1) A 2kW fire left on for 3 hours
48p
2) A 0.2kW TV left on for 5 hours
8p
3) A 0.1kW light bulb left on for 10 hours
8p
4) A 0.5kW hoover left on for 1 hour
4p
Reading Electricity Meters
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1) How many units of electricity
have been used?
2) If 1 unit costs 10p how much
has this electricity cost?
The 9 types of energy
Type
Heat
Kinetic (movement)
Nuclear
Sound
Light
Chemical
Electrical
Gravitational potential
Elastic potential
3 example sources
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The Laws of Physics
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There are many laws of physics, but one of the most important
ones is:
Energy cannot be created or
destroyed, it can only be converted
from one form to another
Energy changes
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To describe an energy change for a
light bulb we need to do 3 steps:
1) Write down the
starting energy:
2) Draw an arrow
Electricity
3) Write down
what energy types
are given out:
Light + heat
What are the energy changes for the following…?
1) An electric fire
2) A rock about to drop
3) An arrow about to be fired
Conservation of Energy
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In any energy change there is ALWAYS some “waste” energy:
e.g. a light bulb:
Electricity
Light
+
heat
In this example HEAT is wasted and it is transferred to
the surroundings, becoming very difficult to use.
Describe the following energy changes and state the “waste”
energy or energies:
1) A vacuum cleaner
2) A TV
3) A dynamo/generator
Efficiency
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Efficiency is a measure of how much USEFUL energy you
get out of an object from the energy you put INTO it.
For example, consider a TV:
Electrical
Energy (200J)
Sound (40J)
Efficiency = Useful energy out
Energy in
x100%
Some examples of efficiency…
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1) 5000J of electrical energy are put into a
motor. The motor converts this into 100J of
movement energy. How efficient is it?
2) A laptop can convert 400J of electrical energy
into 240J of light and sound. What is its
efficiency? Where does the rest of the
energy go?
3) A steam engine is 50% efficient. If it delivers
20,000J of movement energy how much
chemical energy was put into it?
0.2 or
20%
0.6 or
60%
40KJ
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Energy Transfer (“Sankey”) diagrams
Consider a light bulb. Let’s say that the bulb runs on 100
watts (100 joules per second) and transfers 20 joules per
second into light and the rest into heat. Draw this as a
diagram:
“Input” energy
100 J/s
electrical
energy
“Output” energy
20 J/s
light energy
80 J/s heat
energy (given to
the surroundings)
Example questions
Consider a kettle:
2000 J/s
electrical
energy
Sound
energy
Wasted
heat
Heat to
water
1) Work out each energy value.
2) What is the kettle’s
efficiency?
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Consider a computer:
150 J/s
electrical
energy
10 J/s
wasted
sound
20 J/s
wasted
heat
Useful
light and
sound
1) How much energy is converted
into useful energy?
2) What is the computer’s
efficiency?
Reducing Energy Usage
How can we reduce
energy usage?
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OCR 21st Century Science
Unit P3b Revision
Generating energy
Generators (dynamos)
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Electricity is convenient because it can be transmitted over
long distances and can be used in many ways. But how is it
generated? We need to use a “generator”:
Basically, a generator works by
spinning a magnet near a coil of
wire. That’s useful, but how do we
get this magnet to keep spinning?
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Using primary energy sources in power stations
1) A fuel is burned in the boiler
2) Water turns to steam and the steam drives a
turbine
3) The turbine turns a generator – if you want
more electricity you have to burn more fossil fuels
4) The output of the generator is connected to a
transformer
5) The steam is cooled down in a cooling tower and
reused
Efficiency of Power Stations
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Heat
100J
Boiler
85J
Heat
Heat
Turbine
35J
Kinetic
Heat
Generator
30J
Electrical
Nuclear power stations
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These work in a similar way to normal power stations:
The main difference is that the nuclear fuel is NOT
burnt. This means that they produce less pollution
but they do produce radioactive waste instead.
Radioactive Waste - Ionisation
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Radiation is dangerous because it “ionises” atoms – in other
words, it turns them into ions by “knocking off” electrons:
Alpha radiation is the most ionising (basically, because it’s the
biggest). Ionisation causes cells in living tissue to mutate,
usually causing cancer.
Radioactive Contamination
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Simply being “irradiated” by a radioactive material doesn’t
have to be dangerous – for example, we have background
radiation around us all the time. However, being
“contaminated” is far more dangerous. Consider the example
of Alexander Litvinenko who was poisoned with polonium-210:
Timeline of Events
Video of risks from polonium 210
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Other ways of generating electricity
Can we drive the turbine directly
without burning any fossil fuels? Here
are some examnples...
Wind Power
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Wave Power
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Hydroelectric Power
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The National Grid
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Electricity reaches our homes from power stations through
the National Grid:
Power station
Step up
transformer
Step down
transformer
Homes
If electricity companies transmitted electricity at 230 volts
through overhead power lines there would be too much energy
loss by the time electricity reaches our homes. To ensure this
doesn’t happen, electricity companies transmit electricity at
higher voltages instead.
Which power station?
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Type of
power station
Commissioning costs
Running costs
(p per KWh)
Decommissioning costs
Life span
(years)
Coal
£650 million
4
£100 million
40-80
Oil
£700 million
12
£100 million
40-80
Gas
£800 million
6
£100 million
30-40
Nuclear
£2 billion
3
£500 million
30-40
1) Which power station is the most expensive to build and
why?
2) Give one advantage of coal power stations
3) Why is nuclear fuel cheaper than oil?
4) Overall, which power station is the most expensive?
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Matching supply and demand…
Hydroelectric power
station might “kick in” here
“Baseline” power stations
Solar Panels and Thermal Towers
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What are the
advantages and
disadvantages of solar
power?
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Using Solar Energy in remote places
Geothermal Energy
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Geothermal energy can be used in _______ areas such as
______. In a geothermal source cold water is pumped down
towards ____ _____. The water turns to steam and the
steam can be used to turn ______. In some areas the _____
rising at the surface can be captured and used directly.
Words – steam, Iceland, volcanic, turbines, hot rocks
Non-renewable energy sources
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Advantages
Disadvantages
Cheap fuel costs
Costs a lot of
money to
decommission a
nuclear plant
Good for “basic
demand”
Reliable
Coal, oil, gas and
nuclear
Fuel will run
out
Short start-up time for
gas and oil
Nuclear produces little
pollution
Pollution – CO2 leads to
global warming and SO2
leads to acid rain
Renewable energy sources summary
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Advantages
Disadvantages
Zero fuel costs
Unreliable
(except for
hydroelectric)
Don’t produce
pollution
Hydroelectric
is good for a
“sudden”
demand
Solar is good for
remote locations
(e.g. satellites)
Wind, tidal,
hydroelectric and solar
Expensive
to build
Tidal barrages destroy the
habitats of wading birds
and hydroelectric schemes
involve flooding farmland
Electricity Supply in the UK
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Notice that, due to all these advantages and disadvantages, we
use a variety of sources of energy in the UK: