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Electromagnetic Spectrum

Notes

  • Electromagnetic spectrum consists of seven kinds of waves
    • radio waves
    • microwaves
    • infra-red radiation
    • visible light
    • ultraviolet radiation
    • X-rays
    • gamma rays


  • The shorter the wavelength, the higher the frequency.

Properties of electromagnetic waves
  • They are all transverse waves.
  • They transfer energy from one place to another.
  • They all show wave properties such as reflection and refraction.
  • They can all travel through a vacuum
  • They all travel at a speed of 3 x 108 ms-1 in a vacuum.
  • The equation [wave speed = frequency x wavelength] applies to them.

Uses of electromagnetic waves

Effects of electromagnetic waves on cells and tissue
  • High energy electromagnetic waves (those with higher frequencies) can ionize atoms and molecules of living matter, causing damage to body cells.
 Type    Waves Effects of absorption 
 IonizingGamma rays
X-rays 
  • Ionizations can cause DNA damage in body cells
  • mutating effect to future generations
  • cause cancer 
 Non-ionizingUltraviolet
Visible light
Infra-red
Microwaves
Radio waves 
  • heating of body surface

MCQ

1. Which of the following make(s) use of ultraviolet radiation?
(1) scanning to see an image of a developing baby inside the womb
(2) treating cancer
(3) sterilisation

a. (3) only
b. (1) and (2) only
c. (1) and (3) only
d. (2) and (3) only

2. Which of the following electromagnetic waves will cause heating?
(1) radio waves
(2) infrared radiation
(3) X-rays

a. (2) only
b. (1) and (2) only
c. (2) and (3) only
d. (1), (2) and (3)

3. Which of the following statements about electromagnetic waves is/are true?
(1) radio waves have the shortest wavelengths in the electromagnetic spectrum
(2) gamma rays have the highest frequencies in the electromagnetic spectrum
(3) infrared radiation has a longer wavelength than ultraviolet radiation

a. (1) and (2) only
b. (1) and (3) only
c. (2) and (3) only
d. (1), (2) and (3)

4. Which of the following statements about electromagnetic waves is/are true?
(1) electromagnetic waves travel at the same speed in any medium
(2) all electromagnetic waves can ionise living cells
(3) all electromagnetic waves are transverse waves

a. (3) only
b. (1) and (3) only
c. (2) and (3) only
d. (1), (2) and (3)

MCQ Answers

1.a
2. d
3. c
4. a
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