GCSe Physics - Part 1B

Key points, key words, equations and examiners tips

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  • Created by: Katy Head
  • Created on: 16-05-11 20:56

The electromagnetic spectrum

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
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Gamma Rays and X-rays

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


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Light and Ultraviolet Radiation

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
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Infra-red, mocrowaves and radio waves

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
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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
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Analogue and Digital signals

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
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Observing Nuclear Radiation

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
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Alpha, Beta and Gamma Radiation

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
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Half Life

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
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Radioactivity at work

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
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The Exapanding Universe

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
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The Big Bang

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
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Looking into Space

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
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