1. Generating Electricity
Heat transfer
Evaporation
Infrared Radiation
Generating Electricity
Particles
Efficiency
Heating/
Insulation
Electrical Energy
Red-shift
EM Spectrum
Waves
Big Bang
Formulae
Interpreting graphs
Checking answers
How science works

2. 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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3. 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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4. Particles Back 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.
Conduction, convection, evaporation and condensation all transfer energy, and all involve particles in their theories.
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 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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5. Evaporation
Particles can gain kinetic energy through heating but that energy has to come from somewhere
The particles need lots of kinetic energy to overcome these forces
Particles in a liquid are held together by forces
So your skin is losing energy through heating the particles and it will feel colder.
Liquids on your skin get the energy they need for evaporation from your skin.
If particles are leaving the liquid on your skin through evaporation, they are taking kinetic energy with them.
The average kinetic energy of the liquid on your skin has dropped.
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6. Heating and Insulation
Insulation materials aim to reduce energy transfer by heating – they may reduce conduction, convection, and radiation.
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
Liquids on your skin get the energy they need for evaporation from your skin.
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 U-value, the better the material is as an insulator.
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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7. Efficiency 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%)

8. Efficiency Sankey diagrams are often used to show efficiency
Efficient:
Not efficient:
Most energy is transferred to a useful form.
Most energy is transferred to a non-useful form – it is wasted.
The ratio of useful energy transferred to total energy in gives you the efficiency of the machine represented by the Sankey diagram.
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9. Generating Electricity
Power stations heat water to make steam  steam turns a turbine  the turbine spins a generator
Heat can be generated by:
burning fossil fuels
nuclear fission
burning biofuels
Water and wind can drive a turbine directly (no need for heating)
At night, power stations still generate electricity. Fewer people use electricity at night (they’re asleep…) so the supply of electricity is much greater than the demand.
Electricity companies can therefore sell electricity for less during the night.
The Sun’s energy can be used to generate electricity (either by heating water or directly)
Different methods of generating have different effects on the atmosphere
Small-scale generation is useful in remote areas.
National grid – a grid of cables and transformers transferring electrical energy around the country
Step-up transformer  voltage up, current down  lower current means less heating in cables  less energy wasted in the cables
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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10. Electrical Energy Back Back Energy transferred = power x time
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 = power x time
E (kWh) = P (kW) x 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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11. Waves
Waves transfer energy
Transverse
Vibrations are perpendicular to the direction of energy transfer
Longitudinal
Vibrations are parallel to the direction of energy transfer.
Compressions – where the lines are close together.
Rarefaction – where the lines are spread out.
Electromagnetic waves are transverse.
Sound waves are longitudinal.
Mechanical waves can be either.
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)
angle of incidence = angle of reflection
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Wave speed (m/s) = frequency (Hertz) x wavelength (metres)
v = f x λ

12. Electromagnetic Spectrum
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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13. Big Bang Theory Back Back 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
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 (evidence for Big Bang theory)
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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14. 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
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.
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.
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15. Formulae The formulae you need to use will (probably) be given to you
You should be able to rearrange the formulae when asked
After that, all you need to do is put in the numbers
Y = X Z
Z = X Y
If X = Y x Z
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16. How science works
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.

17. How science works
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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18. Interpreting graphs
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

19. Interpreting graphs What does this graph tell you?
Temperature (oC)
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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20. Checking your answers
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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