- Created by: Rosanna Weatherly
- Created on: 16-06-11 17:13
They all travel at the speed of light. It goes from long to short in length.
Radio - Very long,low energy, low frequency waves. Can't penetrate the ionosphere. Used for communication. The longer the length the better it defracts around corners.
Micro - Can penetrate ionosphere, used for sending information (e.g texts, emails) to satellites. Can be used to cook food
Infrared - Everything above absolute zero has this. It releases heat. Used in ovens, and detectors use it to find things eg criminals
Visible Light - Used for seeing things. The only EM wave humans can see. Made up of the rainbow colours which make white light. Used for communication - fibre-optic cables
Ultraviolet - Used for disinfecting foods. Can cause skin cancer by strong doses eg the sun, sunbeds
X-ray - Used in hospitals. Can penetrate skin, but not metal or bone, therefore showing them. Can damage tissue.
Gamma - shortest, highest frequency, highest energy. In low doses gamma can cause cancer by altering cell structure and growth, but in high doses it can cure cancer.
Energy and Heat Transfer
There are 9 types of energy: light, sound, thermal, kinetic, elastic, electric, gravitational potential (GPE), chemical and nuclear.
In exams they may ask why the amount of energy input into a device is the same as all output (not just useful output). The best answer to go with on this is The law of conservation of energy states that energy may neither be created nor destroyed. No energy is lost, simply used inefficiently.
Most of the types of energy are self explanatory, but nuclear energy is a stored energy from the nuclei of an atom which can be released by nuclear reactions.
Chemical energy is stored energy (in food, batteries, fuel etc) can be released by a chemical reaction like burning or respiration.
The proportion of the energy that is converted into something useful is called efficiency. To work it out you divide the amount of useful energy given by the total input of energy.
Generating Electricity - Intro and Non renewable
Electricity is the movement of electrons around a circuit.
A type of energy (eg heat) is used and turned into kinetic energy. The kinetic energy is made by turning water into steam which turns a generator which turns a dynamo. This then makes electricity.
There are 2 main ways to make electricity - from renewable and non renewable sources.
Non-Renewable - Coal, Oil, Gas & Nuclear. The first 3 are burned to create steam. Nuclear is when radioactive atoms are involved in nuclear reactions which create heat (to boil water).
They are good because they are reliable and C, O&G have a low start up cost. Nuclear fuels do not give out carbondioxide or sulphur dioxide.
They are bad because C, O&G give out carbon & sulphur dioxide which contribute to global warming & climate change. Nuclear waste is produced which is harmful to humans and the environment. Decommissioning is expensive.
Generating Electricity - Renewable
Renewable energy power stations -geothermal, solar, wind, tidal and hydro electric.
Geothermal is when heat from the ground is used. In volcanic areas when steam is already at the surface it is just used straight away. In places with hot rocks, cold water is pumped down. They can only be placed in some areas
Solar converts light energy into electrical energy straight away through water in pipes. It uses changes in density to use the water. Solar panels use free energy but are inefficient.
Wind power uses the wind to turn the turbine straight away without the need for heat. They are unreliable, because they don't work with no wind
Tidal barrages are full of generators, which are turned by the sea. They are reliable but are harmful to wildlife
Hydro electricity is when damns are built and opened. GPE in the water is used to turn the turbines (the water falls down). They are reliable but flood farmland
Origins of the Universe.
The Big Bang Theory is the main theory used to explain the origin of the Universe today. This theory is that the whole Universe started from a tiny point and rapidly expanded outwards, and is still expanding today.
Some evidence for this is called Red Shift. This is when light from far galaxies is shifted towards the red end of the spectrum, meaning the frequency is slightly lower and the wavelength is slightly higher. This is linked to the Doppler Effect, which is like when a car is police car is moving and the siren sounds different before & after it goes past. The closer the distance between you and it, the more frequent the wave is.
Red shift helps explain the Big Bang because all the stars in the sky we've observed are red shifted compared to the Sun. The ones which are further away are more red shifted, meaning they are traveling away from us faster than the closer ones.
There are 3 types of telescopes - Optical, Radio and X-Ray.
Optical telescopes are both on Earth and in space. There are used for observing visible light in space using mirrors and glass.
On the ground optical advantages are they are easily fixed and maintained. They are also easier to build. Disadvantages are that they don't work if it's cloudy, they can only be used at night and the atmosphere absorbs some light from space.
Optical space telescopes have clearer pictures (no atmosphere)and you can use them all the time. However they are difficult to make, maintain and fix.
Radio telescopes detect radio waves from space. Advantages are they can be used in any weather and you can use them in the night & day. Disadvantages are they are very big & expensive
X-ray telescopes detect x-rays from space. Because the Earth's atmosphere partially absorbs x-rays they have to be in space, meaning maintenance is difficult and expensive.
Radioactivity is about atoms and their structure.
Alpha radiation is positively charged and not very penetrative (it's absorbed by paper) but is highly ionising, so is not used for medical tracers. It is the nucleus of a helium atom.
Beta radiation is negatively charged and fairly penetrative (it's absorber by skin and thick aluminium). Beta is used in machinery to test thickness of things. It is a high energy electron given out when a neutron decomposes.
Gamma is neutrally charged, highly penetrative and can cause cancer. It is a wave, not a particle. Thick lead absorbs it.
An isotope is an atom which has a different number of neutrons to another atom of the same, meaning the atomic mass, but not the element is different
The half-life of a radioactive isotope is the time taken the radioactive decay to decrease by half.
Optical fibres can carry information coded in light or infrared signals. Optical fibres can carry more information than an ordinary cable of the same diameter.
Total internal reflection is used, meaning the light is reflected all the way along the tube to get to the end. The signal doesn't weaken.
Analogue signals vary continuously in frequency and amplitude. When analogue signals pick up noise and it gets amplified.
Digital signals are discrete - they are either one or the other, on or off. They maintain quality better than analogue signals and carry more information per second.
Conduction, Convection, Radiation
Heat is transferred by conduction, convection and radiation.
Conduction is through solids, and when its a metal electrons carry energy too. The particles vibrate and pass extra kinetic energy to the next particle. This then turns into heat.
Convection is through liquids and gasses. It's when the particles move until it finds others to pass on the extra energy.
Radiation is not anything to do with particles, but is a wave. It is the only one of the three which can travel through a vacuum, like space.
Black is a good absorber and emitter of heat
White is not a good absorber and emitter of heat
Silvered surfaced reflect radiation, so are used in thermos flasks.