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What are electromagnetic waves?

What’s the connection between light, microwaves and X-rays?

Electromagnetic waves are transverse waves made up of electric and magnetic fields.

magnetic field

electric field

wave direction

They are all different types of electromagnetic radiation that travel as waves and transferenergy from one place to another.

All electromagnetic waves travel at the same speed.

In a vacuum (space), they travel at 300,000,000 m/s!


Some definitions…

1) Amplitude – this is “how high” the wave is:

2) Wavelength () – this is the distance between two corresponding points on the wave and is measured in metres:

3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz)


How do electromagnetic waves differ?

Different electromagnetic waves carry different amounts of energy.

The amount of energy carried by an electromagnetic wave depends on the wavelength: the shorter the wavelength, the higher its energy.

Do microwaves have a shorter wavelength than X-rays?

For example, microwaves carry less energy that X-rays.

Wavelength and frequency are linked properties of a wave: the shorter the wavelength, the higher its frequency.

So, frequency also tells you about the energy of a wave: the higher its frequency, the higher the energy.


What happens when waves hit a surface?

When electromagnetic waves hit a surface, they can be reflected, absorbed or transmitted.

How the waves behave, depends on their energy and the type of material.

For example, light waves are reflected by skin but X-rays pass straight through.

If electromagnetic waves are absorbed, some of their energy is absorbed by the material. This usually increases the temperature of the material.


What happens when waves are reflected?

Some surfaces can reflect electromagnetic waves. Shiny surfaces are good reflectors of light waves.

A mirror reflects most of the light waves that hit it.

When waves are reflected, some of their energy may also be absorbed by the material.

The curved satellite dish reflects microwaves from a satellite to the receiver.

How does reflection allowus to see?


What is the electromagnetic spectrum?

The electromagnetic waves are grouped into types that have similar wavelengths and so have similar properties.

Electromagnetic waves form a continuous series in order of changing wavelength, frequency and energy. This series is called the electromagnetic spectrum.

gamma raysX-raysultraviolet

visible lightinfraredmicrowaves

radio waves

0.01 nm100 nm 1 nm0.01 mm1 mm10 cm100 m

smaller wavelength higher frequency, energy and hazard.


The electromagnetic spectrum


Wavelength of electromagnetic waves


Are electromagnetic waves dangerous?

The shorter the wavelength (and higher the frequency) of electromagnetic waves, the more energy that they carry.

gamma raysX-raysultraviolet

visible lightinfraredmicrowaves

radio waves

energy increases

hazard increasesHigh-frequency electromagnetic waves, such as gamma rays, are potentially more harmful because they have more energy.

0.01 nm100 nm 1 nm0.01 mm1 mm10 cm100 m


Energy of electromagnetic waves


How do radio waves affect humans?

Radio waves are the longest-wavelength electromagnetic waves and mostly pass through the body.

Microwaves are radio waves with short wavelengths. They are very slightly absorbed by the body and can cause a minor heating effect.

They are not strongly absorbed and are thought to have no effect on the health of living tissue.

However, the microwaves produced by mobile phones have not yet been proved to cause health problems.


How do infrared waves affect humans?

Infrared waves are absorbed by skin to a limited depth. They transfer their energy to the skin tissue warming it up.

Infrared waves from this grill heat the surface of the meat. If the meat absorbs too much energy, it will become burnt.

it will become burnt.

If skin is exposed to too many high-energy infrared waves,

This heating effect is detected by temperature-sensitive nerve endings in the skin.


How does visible light affect humans?

Your eyes detect visible light, which does not normally pose any health risk.

Lasers are very intense sources of visible light. The lasers used in light shows are not powerful enough to cause harm but must be used safely.

However, very bright light can damage your eyes and may even make you blind. This is why you should not look at the Sun through a telescope or binoculars.

Some very powerful lasers can cut through materials such as metal. These would also be able to burnthrough living tissue.


How do ionizing waves affect humans?

Ionizing waves have enough energy to ionize the atoms in materials. These waves can have a severe effect on living tissue by killing cells or damaging DNA.

Ultraviolet rays are absorbed by the body. Skin tissues can be ionized and damaged by the shortest-wavelength ultraviolet radiation causing skin cancer.

X-rays pass through soft body tissue, such as skin and muscle, without being absorbed. Denser tissue, such as bone, absorb some X-rays and can be ionized.

Gamma rays pass through the body but very high energy waves can ionizeatoms in living tissue.


Effect of electromagnetic waves


Glossary (1/2)

absorption – The process in which electromagnetic waves hit a surface and their energy is transferred to the material.

electromagnetic spectrum – The continuous series of electromagnetic waves in order of wavelength or frequency.

frequency – The number of waves passing a point every second, measured in hertz (Hz).

gamma rays – Electromagnetic waves with the shortest wavelengths. Uses include sterilizing medical equipment and cancer treatment.

infrared waves – Electromagnetic waves given off by hot objects. Uses include heating, cooking and remote controls.

microwaves – Electromagnetic waves that are short-wavelength radio waves. Uses include mobile phones, radarand cooking.


Glossary (2/2)

radio waves – Electromagnetic waves with the longest wavelengths. Used for communications.

reflection – The process in which electromagnetic waves bounce back from a surface.

wavelength – The distance between two matching points on neighbouring waves, which is measured in metres.

ultraviolet rays – Electromagnetic waves that can be absorbed by certain chemicals and emitted as visible light. Uses include tanning beds and security marking.

visible light – Electromagnetic waves that are detected by our eyes, allowing us to see. Other uses include optical fibre communications and imaging.

X-rays – Electromagnetic waves that pass through most

materials. Uses include medical imaging and security.


Anagrams


Multiple-choice quiz


The electromagnetic spectrum

How many different electromagnetic waves can you spot?


Some answers…

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