GCSe Physics - Part 1B

Key points:-

• The electromagnetic spectrum (in order of increasing wavelength): Gamma rays, X-rays, Ultra-violet, visible, infra-red, mocrowaves and radio waves
• All electromagnetic waves travel through space or a vacuum at a speed of 300 million metres per second
• Wave speed (metres per second) = frequency (hertz) * wavelength (metres)

Key words:- electomagnetic spectrum, wave speed, wavelength, frequency

Examiners Tips:-

• Electromagnetic waves transfer energy and not matter
• Examination questions often come up about the electromagnetic spectrum. Make sure you can put the parts of the spectrum in the correct order

Key Points :-

• X-rays and Gamma radiation are absorbed by dense materials in bone and by metal
• X-rays and Gamma radiation damage living tissue when they pass through it
• X-rays are used in hospital to take radiographs
• Gamma Rays  are used to kill harmful bacteria in food, to sterilise surgical equipment and to kill cancer cells

Key words:- Gamma rays, X-rays, dose, cancer

Examiners tips :-

• Gamma radiation can cause cancer but it is also used to treat cancer

Key Points :-

• Ultraviolet radiation is in the electromagnetic spectrum between visible light and X-rays
• Ultraviolet radiation has a shorter wavelength than visible light
• Ultraviolet radiation can harm the skin and the eyes

Key words:- Ultraviolet, fluorescent, visible, optical fibres

Examiners tips:-

• Make sure you can explain in detail some applications and hazards of Ultraviolet radiation

Key points:-

• Infra-red: Heaters, communications (remote handsets, optical fibres)
• microwaves:  Microwave ovens, communications
• radio waves: communications

Key words:- infra-red radiation, microwaves, radio waves, communications, optical fibres, transmitters.

Examiners tips:-

• Make sure that you can explain the effects of different wavelengths of electromagnetic radiation on living cells
• Knowing the detail here is important - it will gain you extra marks

Key Points :-

• The use we make of radio waves depends on the frequency  of the waves
• Visible light  and infra-red radiation are used to carry signals in optical fibres

Key words:- communications, optical fibres, reflections

Examiners tips:-

• Remember that the radio wave part of the electromagnetic spectrum covers a large range of frequencies; from 3000 million Hz to less than 300,000 Hz.
• The range of wavelengths is 0.1 metre to more than 1 kilometre

Key Points :-

• Analogue signals vary continuously in amplitude
• Digital signals are either high (1) or low (0)
• Digital transmission, when compared with analogue transmission,  is free of noise and distortion. It can also carry much more information.

Key words:- Analogue, Digital, noise, amplitude, amplified, distortion

Examiners tips:-

• In this context, 'noise' means unwanted, usually random, impulses that get added to the original signal
• Remember that digital signals can carry much more information than analogue signals
• Digital pulses can be made very short so that many pulses can be transmitted each second

Key points:-

• A radioactive substance contains unstable nucleii
• An unstable nucleus becomes stable by emitting radiation
• There are three main types of radiation from radioactive substances
  • Alpha, Beta and Gamma radiation
• Radioactive decay is a random event - we cannot predict or influence when it will happen

Key words- nucleii, proton, neutron, electron, radioactive decay, alpha particles, beta particles, gamma rays

Examiners tips :-

• Radioactive decay is a random process - it is not possible to predict when any particular nucleus will decay and it is not possible to make any particular nucleus decay
• Radioactive decay is not effected by external conditions. You cannot make it happen faster by changing things like temperature or pressure

Key points:-

• Alpha radiation is stopped by paper or a few centimetres of air
• Beta radiation is stopped by thin metal or about a metre of air
• Gamma radiation is stopped by thick lead and has an unlimited range in air

Key words:- ionisation, electric and magnetic fields, charge

Examiners tips:-

• For each of the three types of radiation you need to remember
  • what it is
  • how ionising it is
  • how far it penetrates different materials
  • if it is deflected by electric and magnetic fields

Key points :-

• The half-life of a radioactive substance is the time it takes:-
  • for the number (and therefore the mass) of parent atoms in a sample to halve
  • For the count rate from the original substance to fall to half its original level

Key words:- half life, count rate

Examiners tips:-

• Practice doing half-life calculations

Key points:-

• The use we can make of a radioactive substance depends on :-
  • its half-life
  • the type of radiation it gives out

Key words :-  tracers

Examiners tips :-

• For each radiation you should know an application why a particular source is used and the approximate half-life

Key Points:-

• Light from a distant galaxy is red shifted to longer wavelengths
• The further away the galaxy the bigger the red shift

Key words:- red shift, galaxies

Examiners tips:-

• The further away a galaxy is from us the faster it is moving away from us

Key points:-

• Red shift provides evidence that the universe is expanding
• The universe started with the Big Bang, a massive explosion from a very small point

Key words:- expanding, Big Bang

Examiners tips-

• Be sure you can explain why red shift is evidence for an exanding universe and the Big Bang

Key points :-

• Observations are made with telescopes that may detect visible light or other electromagnetic radiations
• Observations of the Solar System and galaxies can be carred out from the Earth and from Space

Key words:- telescope, atmosphere, satellite

Examiners tips :-

• Not all telescopes detect visible light, Some 'see' into Space by detecting radiation from other parts of  the electromagnetic spectrum