GCSE Physics - P2 Radiation & Life - Revision Notes

My revision notes on GCSE Physics - OCR 21st Century Science - P2 Radiation & Life. Hope they help!

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P2 ­ Radiation and Life - Revision Notes
Light is a type of electromagnetic (EM) radiation, radiation is just a transfer of energy. For example,
sunlight is a transfer of energy from the sun to the earth. Visible light (the colours of the rainbow,
can be written as red visible light violet) is radiation that out eyes can detect. Seven types of radiation
make up the electromagnetic spectrum.
EM radiation can also be called electromagnetic waves, as in microwaves and radio waves.
All types of EM radiation transfer energy. For example, you can feel the warmth of the sun because
heat energy is travelling through space as infrared radiation. This energy is delivered as photons; a
photon is a tiny `packet' of energy.
Each photon carries a small amount of energy, but not all photons have the same amount of energy.
The amount of energy carried by a photon depends on the frequency of the radiation. The frequency
(and therefore photon energy), increases as you go along the electromagnetic spectrum. Radio wave
photons have the lowest frequency and so least amount of energy, gamma rays have the highest
frequency and so the most energy.
Lots of objects emit EM radiation, e.g. Mobile Phones, Microwave Ovens, etc. The frequency of
thermal radiation emitted from an object increases with temperature. Once emitted, all types of EM
radiation can travel through space (a vacuum). In a vacuum, all EM radiation travels and the same
speed, the speed of light. The speed of light in a vacuum is about 300,000km/s or 3.0 x 10 8m/s.
1. When emitted from a source, radiation spreads out until it reaches some matter. Three
different things can happen. The radiation can be Transmitted, just keep going, Reflected,
bounce back or Absorbed, like a sunbather absorbing UV rays from the sun.
2. What happens depends on what the substance is like and the type of radiation.
3. Two or three of these things can happen at the same time. For example, when sunlight
shines on glass, a lot of the light is transmitted, but some of it is reflected.
4. Radiation can be absorbed by objects a long way from the source, like when a parked car
warms up it the sunshine.
5. Objects that absorb radiation are called detectors ­ our eyes are light detectors.
When radiation is absorbed by matter, the photons transfer their energy to the matter, the energy
`deposited' by a beam of photons depends on how many photons there are and the energy of each
photon (total energy = number of photons x energy of each photon). The intensity of radiation
means how much energy arrives at each square metre of surface per second, the units of intensity
are W/m2 (watts per square metre). The intensity of a beam of radiation decreases from the source;
this is because the beam spreads out and gets partially absorbed as it travels. For example, as
infrared radiation from the sun travels through space and the atmosphere, it spreads out and some
is absorbed or reflected back by the atmosphere. So the radiation is less intense on earth than on
mercury, which is closer to the sun as has no atmosphere.
1. All substances are made up of molecules or atoms.

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When a photon hits a molecule or atom, it sometimes has enough energy to remove an
electron and change the atom or molecule.
3. This process is called ionisation.
4. The changed atoms or molecules can go on to initiate (start) other chemical reactions.
5. It takes lots of energy to remove an electron from an atom or molecule. So only the types of
radiation with high enough photon energy can cause ionisation ­ ultraviolet, x-rays and
gamma rays.…read more

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Microwaves are used to send signals between mobile phones and mobile phone masts.
2. When someone makes a call on a mobile, the phone emits microwave radiation. Some of
this radiation is absorbed by their body, this causes heating of body -=tissues (which all
contain water).
3. There are concerns that heating of tissues like the brain and jaw could increase the risk of
some medical conditions, possibly including cancers. However, there is no conclusive
evidence to show this.
4.…read more

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So the ozone layer is very important ­ it protects us from too much UV
Two of the greenhouse gases which keep the earth warm are carbon dioxide (CO) and methane
(CH). There's a small amount of CO and just trace amounts of methane, both of these gases
contain carbon.
All of the carbon on the earth moves in a big cycle.
Some processes return CO to the atmosphere as part of this carbon cycle:
Respiration in animals and plants.…read more

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People's lifestyles have changed, all this needs energy, which we get mainly from burning
fossil fuels, which releases more CO.
2. The population is on the rise, so more land is needed to build houses and grow food, this
space is sometimes made by chopping down and burning trees, this also add to the CO
levels in the atmosphere:
Plants are the main things that remove carbon dioxide from the atmosphere, so
fewer trees means less CO is taken out of the atmosphere.…read more

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Global warming has changed weather patterns in many parts of the world. It's thought that
many regions will suffer from more extreme weather because of this. Hurricanes form over
water that's warmer than 27°C, so more hurricanes are expected.
The extra heat in the atmosphere will also increase convection (stronger winds) and result in
more water vapour (more rain), causing more storms and floods.…read more

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Digital signals can only take one of a small number of discrete values (usually 2), e.g. 0 or 1,
True or False, Off or On.
3. The information is carried by switching the EM carrier on or off.
4. This creates pulses, shorts bursts of waves.
5. A digital receiver will then decode these pulses to gt a copy of the original signal.
Both digital and analogue signals weaken as they travel, so they may need to be amplified along
their route.…read more


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