Describe the harmful effects on people of excessive exposure to electromagnetic radiation, including: (a) microwaves; internal heating of body cells (b) infrared; skin burns (c) ultraviolet; damage to surface cells and eyes, leading to skin cancer an

3.3 Electromagnetic Spectrum – Harmful Effects of Excessive Exposure

Electromagnetic (EM) radiation spans a wide range of wavelengths and frequencies. While many parts of the spectrum are harmless at normal levels, excessive exposure can damage living tissue. The following notes describe the main health hazards associated with four important regions of the spectrum.

1. Microwaves

Microwaves have wavelengths from about 1 mm to 1 m (frequencies 300 MHz to 300 GHz). They are commonly used in communication, radar and microwave ovens.

• Microwaves are absorbed primarily by water molecules.
• Absorption causes rapid rotation of polar molecules, converting EM energy into heat.
• Excessive exposure can lead to internal heating of body cells, potentially raising tissue temperature and causing burns deep within the body.

2. Infrared (IR)

Infrared radiation lies between 700 nm and 1 mm (frequencies 300 GHz to 430 THz). It is emitted by warm objects and is used in heating, remote controls and thermal imaging.

• IR is strongly absorbed by the outer layers of skin.
• Prolonged or intense exposure can cause skin burns and damage to superficial tissues.
• Thermal cameras detect IR because it is emitted by bodies with temperature above absolute zero.

3. Ultraviolet (UV)

Ultraviolet radiation covers wavelengths from about 10 nm to 400 nm (frequencies 750 THz to 30 PHz). The Sun is the main natural source; artificial sources include tanning beds and U \cdot lamps.

• UV‑C (10–280 nm) and UV‑B (280–315 nm) have enough energy to break chemical bonds.
• These photons damage surface cells of the skin and the eyes, leading to:

  • Sunburn and increased risk of skin cancer (e.g., melanoma).
  • Eye conditions such as photokeratitis, cataracts and macular degeneration.

• The energy of a photon is given by \$E = h\nu = \frac{hc}{\lambda},\$ where \$h\$ is Planck’s constant and \$c\$ the speed of light.

4. X‑rays and Gamma Rays

X‑rays (0.01–10 nm) and gamma rays (<0.01 nm) have the highest frequencies and energies in the EM spectrum. They are produced by high‑energy processes such as nuclear reactions, radioactive decay and medical imaging equipment.

• These photons are ionising; they can remove tightly bound electrons from atoms.
• Ionisation can cause mutation or damage to cells throughout the body, potentially leading to:

  • Cancer (e.g., leukaemia, thyroid cancer).
  • Genetic mutations that may affect future generations.
  • Acute radiation syndrome at very high doses.

• Protective measures include lead shielding and limiting exposure time.

Summary Table of Harmful Effects