Uses and Dangers of Electromagnetic Waves

Each band is used for what its wavelength and energy suit it to, and its dangers follow from the same properties.

Radio waves — broadcasting radio and television, and communication with ships and aircraft. They diffract around hills and reflect off the ionosphere, so they reach far beyond line of sight. No significant danger; they pass through the body without being absorbed.

Microwaves — cooking, and satellite communication. In an oven they are absorbed by water molecules in the food, which gain energy and heat the food from within. For satellites the point is the opposite property: certain microwave frequencies pass straight through the atmosphere, so a signal can reach a satellite and return. Danger: absorbed by water in body tissue, causing internal heating.

Infrared — thermal imaging, remote controls, optical fibre communication, electric heaters and grills. Every warm object emits infrared, which is what a thermal camera detects. Danger: skin burns.

Visible light — vision, photography, illumination and fibre-optic communication. Danger: very intense light can damage the retina.

Ultraviolet — fluorescent lamps, security marking that shows up only under UV, detecting forged banknotes, and sterilising water. Danger: ionising. Causes sunburn, premature ageing of the skin, skin cancer, and eye damage including cataracts. Sunscreen and UV-blocking sunglasses are the sensible protection.

X-rays — medical imaging of bones, and airport security scanning. They pass through soft tissue but are absorbed by denser material such as bone and metal, which is what produces the shadow image. Danger: ionising; mutation and cancer. Radiographers stand behind lead screens and patients wear lead aprons, and doses are kept as low as the image allows.

Gamma rays — sterilising surgical instruments and food, detecting and treating cancer, and as medical tracers. Danger: ionising and highly penetrating; cell damage, mutation and cancer.

The pattern worth learning rather than the list. Danger rises with frequency. Below visible light the risk is heating; at ultraviolet and above it is ionisation, which damages DNA and can cause cancer. If you can remember which side of visible light a wave sits on, you can reason out the type of harm.

Example: microwaves and gamma rays both harm tissue, but differently. A microwave oven cooks you; a gamma source mutates you. The distinction is heating against ionisation, and it comes straight from the energy per wave.