CIE IGCSE Physics

Revision Notes

3.3.1 The Electromagnetic Spectrum

Parts & Properties of the Electromagnetic Spectrum

  • Visible light, however, is just one small part of a much bigger spectrum: the electromagnetic spectrum
  • The different parts of the spectrum have different names (and some different properties)
  • These parts are shown in order below, going from the longest wavelength (and lowest frequency) to the shortest wavelength (and highest frequency)

Electromagnetic spectrum, IGCSE & GCSE Physics revision notes

Visible light is just one small part of a much bigger spectrum: The electromagnetic spectrum

  • All electromagnetic waves share several properties:
    • They are all transverse
    • They can all travel through a vacuum
    • They all travel at the same speed in a vacuum
Extended Only

The Speed of Electromagnetic Waves

  • The speed of light, in a vacuum, is approximately 3 x 108 m/s
  • The speed of light in air is approximately the same

Uses of Electromagnetic Waves

  • Electromagnetic waves have a large number of uses. The main ones are summarised in the table below

Electromagnetic waves table, IGCSE & GCSE Physics revision notes

  • Radio waves and microwaves
    • These two parts of the spectrum share a lot of similarities and uses. Their main uses concern wireless communication – in fact many things that people often assume use radio waves actually use microwaves (e.g. WiFi, radar, mobile phones, satellite communications…)
    • At very high intensity, microwaves can also be used to heat things: This is what happens in a microwave oven
  • Infrared
    • Infrared is emitted by warm objects and can be detected using special cameras (thermal imaging cameras). These can be used in industry, in research and also in medicine
    • Many security cameras are capable of seeing slightly into the infrared part of the spectrum and this can be used to allow them to see in the dark: Infrared lights are used to illuminate an area without being seen, which is then detected using the camera
    • Remote controls also have small infrared LEDs that can send invisible signals to an infrared receiver on a device such as a TV
    • Infrared travels down fibre optic cables more efficiently than visible light, and so most fibre optic communication systems use infrared
  • Ultraviolet
    • Ultraviolet is responsible for giving you a suntan, which is your body’s way of protecting itself against the ultraviolet
    • When certain substances are exposed to ultraviolet, they absorb it and re-emit it as visible light (making them glow). This process is known as fluorescence
    • Fluorescence can be used to secretly mark things using special ink – in fact most bank notes have invisible fluorescent markings on them
    • Fluorescent light bulbs also use this principle to emit visible light
  • X-rays
    • The most obvious use of x-rays is in medicine. X-rays are able to pass through most body tissues, but are absorbed by the denser parts of the body, such as bones. When exposed to x-rays, bones create a shadow which can be seen using a special x-ray detector or using photographic film
  • Gamma rays
    • Gamma rays are very dangerous and can be used to kill cells and living tissue
      If the gamma rays are carefully aimed at cancerous tissue they can be very effective at killing it
      Gamma rays can also be used to sterilise things by killing off the bacteria

Dangers

  • Electromagnetic Waves can have some harmful side effects. In particular:

Microwaves

  • High levels of microwaves can cause heating of internal organs. (Although there is no evidence that the levels emitted by mobile phones or WiFi devices cause any harm)

X-Rays

  • X-rays, Gamma rays and (to a lesser extent) ultra-violet are all ionising. This means that they can cause harm to living tissues: killing cells or possibly mutating them or causing cancer
  • Whilst the levels used in most medical x-rays pose a minimum risk, hospitals are careful to minimise the amount of x-ray exposure that individuals (including hospital staff) receive

EM uses and dangers summary, IGCSE & GCSE Physics revision notes

Uses and dangers of the electromagnetic spectrum

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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