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Summary GCSE Physics OCR 21st Century
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Summarised notes on the following topics: • Chapter P1: Radiation and waves • Chapter P2: Sustainable energy • Chapter P3: Electric circuits
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P1Gamma rays:
➢ Carry the most energy of all electromagnetic waves
➢ Used for medical imaging and therapy, sterilisation and food preservation
➢ Extremely penetrating and damaging to living tissues and cells
➢ Gamma rays can be used to destroy bacteria and tumours
X-rays:
➢ Carries the second most energy
➢ Exposure to this should be kept to a minimum as it is dangerous
➢ People working with X-rays should shield themselves by placing materials between
themselves and the X-rays
➢ X-rays are highly ionizing and can damage body cells, even in low doses
➢ Used for medical and industrial imaging
➢ High energy of this is used to treat cancer
➢ Penetrate soft materials
Ultraviolet light:
➢ In lamps, UV photons give energy to atoms
➢ The atoms then release visible light
➢ In sun tanning UV gives energy to skin cells which then change colour
➢ Used in medical and forensic photography, air purification and disinfection
➢ Exposure to too much ultraviolet light can cause skin burns, skin cancer and cataract
formations in the eyes
Visible light:
➢ Used to see the world around us
➢ We use visible light in optical fibres because it can be internally reflected
➢ We can transmit signals along optical fibres without the signals getting lost
Infra-red radiation:
➢ Frequency is high enough to give energy to particles in food increasing their temperature
➢ Infra-red cameras can detect a range of frequencies that can be shown in different
colours to depict images
➢ Used in TV controls or for security purposes in alarms
➢ Can cause serious skin burns if emitted from high-intensity sources
Microwaves:
, ➢ Have a high enough frequency to penetrate the earth’s atmosphere and to reach satellites
➢ Travel in straight lines through the atmosphere which makes them good for transmitting
signals
➢ Used for satellite communications and transmit signals
➢ Absorbed by water, heating up the water in the process, makes microwaves useful for
cooking food because food contains lots of water
➢ We should reduce exposure as we are made of water to this and shield ourselves between
the source
Radio waves:
➢ Used for radio and TV communications
➢ At high intensities, radio waves can cause internal heating of living tissue with
potentially harmful effects
➢ Radio waves have long wavelengths which can be transmitted around the Earth’s surface
and buildings without interference
Changes in atoms, molecules and nuclei:
➢ Can generate and absorb radiations over a wide frequency range
➢ Changes in molecules- oxygen absorbs ultraviolet to produce ozone which also absorbs
ultraviolet. The ozone layer protects life on earth. Molecules emit and absorb infrared in
ways that strongly affect the climate
➢ Changes in atoms- X-rays, ultraviolet and visible light are generated when electrons in
atoms lose energy and change their state in the atom. High energy ultraviolet, gamma
rays and X-rays have enough energy to cause ionisation when absorbed by some atoms
➢ Changes in nuclei- atoms emit gamma rays when the structure of the nucleus changes
Properties of electromagnetic waves:
➢ Wavelength vs frequency:
➢ As you move from gamma rays to radio waves, the wavelengths increase and the
frequencies decrease
➢ Gamma rays have the shortest wavelength and the highest frequency
➢ Radio waves have the longest wavelength and the lowest frequency
➢ Wave energy:
➢ Gamma rays also carry the most amount of energy than any other wave
➢ Wave energy increases with frequency
➢ Wave energy decreases with wavelength
➢ Seven types of waves:
➢ Electromagnetic spectrum can be split into seven types of waves
➢ In order of the highest frequency: gamma, X-ray, ultraviolet, visible, infrared,
microwave and radio waves
➢ All electromagnetic waves travel at the same speed in a vacuum
Production of electromagnetic waves:
➢ Can be produced by electrical circuits and by changes in atoms
➢ Changes in atoms:
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