GCSE — physicsMedium4 min read

Electromagnetic Spectrum

Radio to gamma rays; properties, uses, and hazards of each type

Tutor AI Team
Tutor AI Team

# Electromagnetic Spectrum — GCSE Physics

The electromagnetic (EM) spectrum is the complete range of electromagnetic waves, from low-frequency radio waves to high-frequency gamma rays. Visible light is just a tiny part of this spectrum. Understanding the EM spectrum is essential for GCSE Physics.

1. What Are Electromagnetic Waves?

Electromagnetic waves are transverse waves that transfer energy from a source to an absorber.

Key properties:

  • They are transverse — electric and magnetic fields oscillate perpendicular to the direction of travel
  • They can travel through a vacuum (no medium needed)
  • They all travel at the speed of light in a vacuum: c=3×108c = 3 \times 10^8 m/s
  • They transfer energy — the higher the frequency, the more energy per photon
  • They obey v=fλv = f\lambda, so: high frequency = short wavelength, low frequency = long wavelength

2. The Electromagnetic Spectrum (in Order)

Type Wavelength Frequency Energy
Radio waves > 1 m < 300 MHz Lowest
Microwaves 1 mm – 1 m 300 MHz – 300 GHz
Infrared (IR) 700 nm – 1 mm 300 GHz – 430 THz
Visible light 400 – 700 nm 430 – 750 THz
Ultraviolet (UV) 10 – 400 nm 750 THz – 30 PHz
X-rays 0.01 – 10 nm 30 PHz – 30 EHz
Gamma rays < 0.01 nm > 30 EHz Highest

Memory aid: Richard My Instagram Visual Updates eXcite Grandma

As you move from radio to gamma: wavelength decreases, frequency increases, energy increases.

3. Properties, Uses, and Hazards

Radio Waves

  • Uses: TV and radio broadcasting, Bluetooth, WiFi
  • Hazards: Generally considered safe at normal levels

Microwaves

  • Uses: Microwave ovens (heat food — water molecules absorb the energy), satellite communication, mobile phones
  • Hazards: Can cause internal heating of body tissues

Infrared (IR)

  • Uses: Remote controls, thermal imaging cameras, heaters, fibre optic communication, cooking
  • Hazards: Can cause skin burns; felt as heat

Visible Light

  • Uses: Vision, photography, fibre optic communication, photosynthesis
  • Hazards: Very bright light can damage eyes
  • Colours (longest to shortest wavelength): Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROY G BIV)

Ultraviolet (UV)

  • Uses: Fluorescent lamps, detecting forged banknotes, sterilising water, tanning beds
  • Hazards: Can cause sunburn, skin cancer, eye damage (cataracts)

X-rays

  • Uses: Medical imaging (bones, teeth), airport security, detecting cracks in structures
  • Hazards: Can cause mutations and cancer (ionising radiation); use should be minimised

Gamma Rays (γ)

  • Uses: Sterilising medical equipment, treating cancer (radiotherapy), tracing medical conditions
  • Hazards: Highly ionising — can cause cell damage, mutations, and cancer
  • Produced by radioactive decay and nuclear reactions

4. Ionising vs Non-Ionising Radiation

Ionising radiation has enough energy to remove electrons from atoms (ionise them), which can damage DNA and cause cancer.

  • Ionising: UV (high energy), X-rays, gamma rays
  • Non-ionising: Radio, microwaves, IR, visible light, UV (low energy)

The higher the frequency, the more ionising the radiation.

5. Key Equation

Since all EM waves travel at the speed of light:

c=f×λc = f \times \lambda

Where c=3×108c = 3 \times 10^8 m/s.

Worked Example: Example 1

Problem

Question: Calculate the frequency of red light with a wavelength of 7×10−77 \times 10^{-7} m.

f=cλ=3×1087×10−7=4.29×1014 Hzf = \frac{c}{\lambda} = \frac{3 \times 10^8}{7 \times 10^{-7}} = 4.29 \times 10^{14} \text{ Hz}

Solution

Worked Example: Example 2

Problem

Question: A microwave oven uses microwaves with a frequency of 2.45 GHz. Calculate the wavelength.

λ=cf=3×1082.45×109=0.122 m≈12.2 cm\lambda = \frac{c}{f} = \frac{3 \times 10^8}{2.45 \times 10^9} = 0.122 \text{ m} \approx 12.2 \text{ cm}

Solution

Worked Example: Example 3

Problem

Question: Gamma rays used in radiotherapy have a wavelength of 1×10−121 \times 10^{-12} m. Calculate the frequency.

f=3×1081×10−12=3×1020 Hzf = \frac{3 \times 10^8}{1 \times 10^{-12}} = 3 \times 10^{20} \text{ Hz}

Solution

7. Practice Questions

    1. List the seven types of electromagnetic radiation in order of increasing frequency. (2 marks)
    1. State two properties that all electromagnetic waves share. (2 marks)
    1. Give one use and one hazard of ultraviolet radiation. (2 marks)
    1. Calculate the wavelength of a radio wave with a frequency of 100 MHz. (2 marks)
    1. Explain why gamma rays are more dangerous than radio waves. (3 marks)

    Answers

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Summary

  • EM spectrum: Radio → Microwave → IR → Visible → UV → X-ray → Gamma
  • All travel at c=3×108c = 3 \times 10^8 m/s in vacuum; all transverse
  • Higher frequency = shorter wavelength = more energy
  • UV, X-rays, gamma rays are ionising and can be hazardous
  • Each type has specific uses and hazards
Tags:
#gcse#physics#waves#electromagnetic-spectrum#light#radiation

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