3 Waves – Part C “Electromagnetic Spectrum”

Electromagnetic waves are transverse waves. Their vibrations, or oscillations, are changes in electrical and magnetic fields at right angles to the direction of wave travel.

All electromagnetic waves:

transfer energy as radiation from the source of the waves to an absorber

can travel through a vacuum such as in space travel at the same speed through a vacuum or the air

Electromagnetic waves such as visible light travel at 300,000,000 (3 × 108) metres per second (m/s) through a vacuum.

Some types of electromagnetic waves, like radio waves, microwaves, infrared waves, visible light and ultraviolet waves, can be reflected and refracted. Refraction is caused by differences in the velocity of waves travelling through different substances.

Microwaves

Microwaves are used for cooking food and for satellite communications.

High frequency microwaves have frequencies which are easily absorbed by molecules in food. The internal energy of the molecules increases when they absorb microwaves, which causes heating. Microwaves pass easily through the atmosphere, so they can pass between stations on Earth and satellites in orbit.

Radio waves

Radio waves are used for communication such as television and radio. Radio waves are transmitted easily through air. They do not cause damage if absorbed by the human body, and they can be reflected to change their direction. These properties make them ideal for communications.

Radio waves can be produced by oscillations in electrical circuits. Also, when radio waves are absorbed by a conductor, they create an alternating current. This electrical current has the same frequency as the radio waves. Information is coded into the wave before transmission, which can then be decoded when the wave is received. Television and radio systems use this principle to broadcast information.

Electromagnetic waves in medicine – X-rays and gamma rays.

Changes in atoms and their nuclei can cause electromagnetic waves to be generated or absorbed. Gamma rays are produced by changes in the nucleus of an atom.

They are a form of nuclear radiation. High energy waves such as X-rays and gamma rays are transmitted through body tissues with very little absorption.

This makes them ideal for internal imaging. X-rays are absorbed by dense structures like bones, which is why X-ray photos are used to help identify broken bones.

Visible light

Visible light is the light we can see. It is used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver.

Infrared

Infrared light is used by electrical heaters, cookers for cooking food, and by infrared cameras which detect people in the dark. Security lights and remote controls for TV use infrared waves.

Ultraviolet waves, X-rays and gamma rays are types of ionising radiation. They can add or remove electrons from molecules, producing electrically charged ions. Ionisation can have hazardous effects on cells in the body:

ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer

X-rays and gamma rays can cause the mutation of genes, which can lead to cancer

Ultraviolet

We cannot see ultraviolet (UV) light but it can have hazardous effects on the human body. Ultraviolet light in sunlight can cause the skin to tan or burn and can also damage eyes. Fluorescent substances are used in energy-efficient lamps – they absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light. UV light is also used for banknote security and disinfecting water.

Type

Possible Harmful Effects

Uses

Microwave

Heating of water in tissues (if intense)

Cooking food (penetrates better than IR)

Send signals beyond the ionosphere

UV

Skin cancer / Skin Reddening

Detect forged bank notes / Trainer Sanitiser

X-Ray

Can cause cancer in high intensity

Looking inside the body (X-ray pictures show white and dark areas)

Gamma

Can cause cancer through cell mutations

Can kill cells in the body which are cancerous growth

Use for detection of cracks in metals