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Electromagnetic Radiation

Grade 8 Science Worksheets

Introduction

What does cooking have in common with curing cancer? What does aircraft communication have in common with disinfectants? Remote control devices with night vision goggles? They are all applications of science based on the principles of Electromagnetic Radiation (or EMR).

Radiation is one of the major forms of energy. There is Solar, or Cosmic, Radiationwhich comes from the sun and other objects in outer space (see: Heat and Electromagnetic Energy) and there is Nuclear Radiation from atomic nuclei (see: Nuclear Reactions – Fission and Fusion). EMR is a third major kind of radiation.

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Electromagnetic Waves

EMR consists of Electromagnetic Waves, which travel through space at the speed of light. They are a combination of electric and magnetic energy moving through space, hence the term. These waves vary widely in their Wavelength – the distance between two crests of the wave. Short wavelength EMR has higher energy while long-wavelength EMR carries less energy.

Electromagnetic waves are made up of tiny particles, called Photons, which have been accelerated to great speeds to create high energy packets of energy. Although they travel as a wave, when they strike a substance they behave as individual particles of energy in which each photon has a certain amount of energy.

The main types of Electromagnetic Radiation in increasing order of wavelength (so decreasing order of energy level) are –

  1. Gamma Rays – these have the most amount of energy in the electromagnetic radiation spectrum. They are the result of rearrangement of particles in atomic nuclei, such as the radioactive decay of uranium. They can be generated in nuclear reactors to supply electricity.
  2. X-Rays – these are high energy radiation waves which collide with solid objects and are used by dentists and airport security.
  3. Ultraviolet (UV) light – this is emitted by the sun and is also produced artificially in lamps to sterilize equipment and environment.
  4. Visible Light – this too is a form of EMR obtained from the sun, essential for photosynthesis in plants and for the creation of coal and oil used as energy sources. Life on earth would not exist without visible light.
  5. Infrared Rays – nearly half the sun’s radiant energy is emitted as infrared rays, which are invisible to the eye. They are detected as warmth by the skin.
  6. Microwaves– a form of electromagnetic radiation used in food processing to destroy micro-organisms as well as for rapid and efficient heating of food and other matter at a molecular level.
  7. Radio waves – as the name suggests, these are low energy waves used for sound transmission via radio, as also for aircraft navigation.

All types of electromagnetic waves exhibit the properties of light – for example, they can be reflected or refracted. (See also: Nature of Energy).

Fun Fact: The human body emits radiation in the infrared region due to its temperature, making it possible for night vision goggles to detect human presence in the dark.

Check Point

  1. The three main forms of radiation are ______, ______ and ______.
  2. A wavelength is a distance between two ______ of a wave.
  3. Shorter wavelength EMR has _____ energy level while longer wavelength EMR has ______ energy level.
  4. Electromagnetic waves are made up of tiny particles of matter called ______.
  5. The least amount of energy in the EMR spectrum is carried by –
    1. Infrared light
    2. Radio waves
    3. Microwaves
    4. Gamma rays
    5. Ultraviolet light

Answer Key

  1. Solar, Nuclear, Electromagnetic
  2. Crests
  3. Higher, Lower
  4. Photons
  5. b) Radio waves

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