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02 May 2017
Heat
transfer
Evaporation
Infrared
Radiation
Generating
Electricity
Particles
Heating/
Insulation
Efficiency
EM
Spectrum
Red-shift
Electrical
Energy
Waves
Formulae
Big Bang
How science
works
Interpreting
graphs
Checking
answers
02 May 2017
Energy transfer by heating
• 3 methods – conduction, convection, radiation
• The bigger the temperature difference
between an object and its surroundings, the
faster the rate at which energy is
transferred by heating.
• Rate of transfer of energy depends on
surface area and volume, object materials,
surfaces.
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02 May 2017
Infrared Radiation
• All objects emit and absorb infrared
• The hotter an object is, the more IR it emits
in a given time (time is important!)
• Dark, matt surfaces – good absorbers, good
emitters (this means that a dark, matt object will heat
up faster or cool down faster than a light, shiny one)
• Light, shiny surfaces – poor absorbers, poor
emitters, good reflectors.
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Conduction, convection,
evaporation and
condensation all
transfer energy, and all
involve particles in
their theories.
Particles
In an object, the
more kinetic energy
the particles have,
the hotter the
object is.
Convection Takes place in liquids and gases.
When a liquid or gas gets hotter, the
particles have more KE  they move around
more, making the liquid or gas less dense.
Therefore, hot liquids or gases will rise above
cooler liquids or gases. (HEAT DOES NOT RISE, HOT
02 May 2017
Conduction
All to do with particles
banging into each other
and passing on KE.
Metals have free
electrons which can also
pass on KE, making
metals excellent
conductors. The
arrangement of
particles in a substance
determine how good a
conductor it is.
LIQUIDS AND GASES DO!!)
Particle arrangements:
Solid – fixed in place, least amount of KE but still some movement
Liquid – some fixed arrangement, free to slide over each other, more KE
than solid
Gas – free to move about randomly, no fixed arrangement, lots of KE
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Evaporation
Particles in a
liquid are held
together by
forces
The particles
need lots of
kinetic energy
to overcome
these forces
So your skin is losing
energy through heating
the particles and it will
feel colder.
If particles are leaving
the liquid on your skin
through evaporation,
they are taking kinetic
energy with them.
02 May 2017
Particles can gain
kinetic energy through
heating but that
energy has to come
from somewhere
Liquids on your skin get the
energy they need for
evaporation from your skin.
The average kinetic
energy of the liquid on
your skin has dropped.
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Heating and Insulation
Insulation materials
aim to reduce energy
transfer by heating –
they may reduce
conduction,
convection, and
radiation.
02 May 2017
New heating systems or insulation for a
house cost money. The payback time of an
investment tells you how long it will take to
get your money back based on how much the
investment saves you.
Payback time = initial investment
saving per year
Insulation materials for homes
(including double glazing) are
often given a U-value. This is a
measure of how effective the
insulator is. The lower the Uvalue, the better the material
is as an insulator.
Liquids on your skin get the
energy they need for
evaporation from your skin.
Solar panels sometimes contain
water that is heated by the
Sun. The pipes in a solar panel
are often black. The hot water
can be used for heating.
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Efficiency
02 May 2017
• Two formulae (you’ll be given both)
• Efficiency = useful energy out (x 100%)
total energy in
• Efficiency = useful power out (x 100%)
total power in
• You might need to rearrange these and put
in the numbers.
• Answers can be given either as a
percentage (e.g. 30%) or as a decimal (0.3)
 DO NOT combine these (e.g. 0.3%)
Efficiency
02 May 2017
• Sankey diagrams are often used to show
efficiency
• Efficient:
Most energy is
transferred to
a useful form.
• Not efficient:
The ratio of useful energy
transferred to total energy in gives
you the efficiency of the machine
represented by the Sankey diagram.
Most energy is
transferred to a nonuseful form – it is wasted.
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Generating Electricity
02 May 2017
Power stations heat Heat can be
Water and wind can
water to make
generated by:
drive a turbine directly
 burning fossil fuels (no need for heating)
steam  steam
power
 nuclear
fissionstations still
turns a turbine At night,
the turbine spins
a
 burning
biofuels Fewer people
generate
electricity.
The Sun’s energy can
generator
be used to generate
use electricity
at night (they’re
Different methods
electricity (either by
Small-scale asleep…) of
have of electricity
sogenerating
the supply
heating water or
generation is useful
different effects on
is much the
greater
than the demand.
directly)
in remote areas.
atmosphere
National grid
– a grid of
Step-up transformer
 voltage up,
Electricity
companies
can therefore
cables and transformers
current down  lower current means
sell electricity
less
during
theenergy
transferring electrical
less for
heating
in cables
 less
energy around the country
wasted
in the cables
night.
Step-down transformer  voltage down, current
up  voltage is stepped down to a level which is
safe to use in homes, factories, etc.
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Electrical Energy
02 May 2017
There are a few formulae you should be familiar with (some will be given
to you in the exam).
Energy transferred = power x time
E (Joules) = P (watts) x t (seconds)
Energy transferred in kWh =
E (kWh)
=
power
P (kW)
x
x
time
t (hours)
Cost of using electricity = number of kWh x cost per kWh
Electrical appliances are machines, they transfer energy
from one form to another. For example, a light bulb takes in
electrical energy and gives out light and heat; a hair dryer
takes in electrical energy and gives out heat, sound, and
kinetic energy.
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Waves transfer energy
 Electromagnetic
waves are
transverse.
 Sound waves are
longitudinal.
 Mechanical waves
can be either.
Waves
Transverse
Vibrations are
perpendicular to the
direction of energy
transfer
Waves can be reflected, refracted
(light changing direction), and
diffracted (spread out – much greater
diffraction when the obstruction or
gap is a similar size to the wavelength)
02 May 2017
Longitudinal
Vibrations are parallel
to the direction of
energy transfer.
Compressions – where
the lines are close
together.
Rarefaction – where the
lines are spread out.
angle of incidence = angle
of reflection
Back
Wave speed (m/s) = frequency (Hertz) x wavelength (metres)
v
=
f
x
λ
Electromagnetic Spectrum
02 May 2017
Electromagnetic waves form a continuous spectrum – the EM spectrum
Decreasing wavelength, increasing frequency, waves transfer more energy
All EM
waves
travel at
the same
speed in a
vacuum.
Some of these EM waves can be used for communications:
Radio waves – TV and radio (these can be diffracted by mountains)
Microwaves – mobile phones and satellite TV
Infrared – remote controls and optical fibres
Visible light - photography
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The Big Bang theory
states that…
Everything in the
known Universe was
contained at a very
hot, very dense
initial point. A rapid
expansion took place
around 13.7 billion
years ago in which
space, time and all
matter were
created. There are
2 key pieces of
evidence for this
theory – CMBR and
Red-shift.
Big Bang Theory
02 May 2017
Other theories:
There are other theories for the origins of the
Universe. The Steady State theory suggests
that the Universe has always been huge and is
expanding because matter is entering the
Universe through white holes. However, there is
very little evidence for this theory.
Cosmic Microwave Background Radiation
for Big Bang theory)
(evidence
If you look into space with your eyes, you will
see a lot of emptiness. But if you use microwave
detectors you will see a lot of cosmic microwave
background radiation (CMBR). The existence of
this radiation can only be explained by the Big
Bang theory.
Red-shift is another piece of evidence that the
Universe is expanding because it shows us that
galaxies are moving away from each other.
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Red-shift
Doppler  an object
making a sound is
moving away from
you, the sound waves
stretch out 
wavelength
increases, frequency
decreases
Doppler can also be
applied to light, but
the object emitting
the light needs to be
moving very fast and
huge distances  this
is called Red-shift
Red-shift is one piece of evidence for the
theory that the universe started through a
very rapid expansion (the Big Bang) and is
continuing to expand (CMBR is another piece of
evidence).
The faster a star or galaxy is moving away
from us, the bigger the red-shift will be.
Blue-shift is the opposite to red-shift. If a galaxy is moving
towards us the wavelength of light reduces and the spectrum
of light is shifted towards the blue part of the spectrum.
02 May 2017
Absorption spectra:
These show which
colours of light are
absorbed by, for
example, the
atmosphere of a
planet or the
contents of a galaxy.
The absorbed light is
shown by dark lines
on a colour spectrum.
For a galaxy moving
away from us, these
lines are shifted
towards the red end
of the spectrum.
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02 May 2017
Formulae
• The formulae you need to use will
(probably) be given to you
• You should be able to rearrange the
formulae when asked
If
X=YxZ
Y=X
Z
Z=X
Y
• After that, all you need to do is put in
the numbers
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How science works
02 May 2017
• Bias – if research is funded by a company (e.g. a
mobile phone company) there is the possibility
that the results could be biased, or even not
published if they do not favour the sponsoring
company.
• Reliability – Results are reliable if they are
repeatable by others. Results can be compared
with others to check reliability. Reliability of
data can be improved through collecting lots of
data and calculating an average.
• Sample size – experiments should use as large a
sample of people as possible to get a good
representation of a population.
How science works
02 May 2017
• Control groups – Used in investigations to allow a
comparison to be made.
• Issues:
Ethical – using people (particularly children)
or animals in scientific research
Economic – research being funded by
companies, governments, etc.
Social – how the results of scientific
research affect people
Environmental – research projects can have a
negative impact on an environment even
if there is some benefit (e.g. wind
farms)
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Interpreting graphs
02 May 2017
• Use numbers from the graph to back up
any conclusions
• Use terms and units given to you in the
graph
• Use numbers from the graph as well
• If there is more than one plot on the
graph, compare the plots in your answer
• The graph might show a relationship
between X and Y – i.e. directly/indirectly
proportional
Temperature (oC)
Interpreting graphs
02 May 2017
What does this
graph tell you?
Time (s)
• Red starts at a higher temperature than blue.
• The temperature of red decreases more rapidly
than blue.
• Blue maintains a constant temperature for
longer.
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Checking your answers
02 May 2017
• After you’ve calculated an answer, have a
good look at it and compare it to the
question  does it look right?
• E.g. A student is asked to calculate the
mass of some water being heated in a
beaker. She gets a result of 2.3 x 1012 kg…
• Make sure you use a calculator if you’re not
confident doing it by hand!
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