Electromagnetic waves and radar DA - CCEA

• Recall the 7 different regions of the electromagnetic spectrum.

• Recall the names of the different regions in order.

• Stateapplications and dangers of each region of the EM spectrum.

• Explain how SONAR and RADAR work and perform echo calculations.

Electromagnetic waves are members of a family of waves with common properties called the electromagnetic spectrum.

All electromagnetic waves:

• are transverse waves;

• can travel through a vacuum;

• travel at exactly the same speed in a vacuum, the speed of light, 300,000,000 m/s.

Like all waves, electromagnetic waves:

• transfer energy from one place to another;

• can be reflected.

Differences

Each type of wave in the electromagnetic spectrum has different:

• wavelength;

• frequency .

The electromagnetic spectrum is a continuous range of wavelengths.

The types of radiation that occur in different parts of the spectrum have different uses and dangers - depending on their wavelength and frequency.

There are seven members of electromagnetic family.

Radio waves have the lowest frequencies and longest wavelengths, while gamma waves have the highest frequencies and shortest wavelengths.

All of these waves travel at the same speed in a vacuum, which is the speed of light or about 300,000,000 m/s (metres per second).

Key fact

It is important to remember the order of the seven regions of the electromagnetic spectrum.

The following sentence might help: Rats and Mice In Venice Use eXtra Gondolas.

Over-exposure to certain types of electromagnetic radiation can be harmful.

The higher the frequency of the radiation, the more energy it carries and the more damage it is likely to cause to the body.

• Radio waves can cause a very small rise in the temperature of the human body - of up to 0.2^oC. Some people claim the very low frequency radio waves from overhead power cables and mobile phone base stations near their homes has affected their health, although this has not been reliably proven.

• Microwaves can cause internal heating of body tissues. The microwaves are absorbed by water molecules and vibrate vigorously, causing a rise in temperature.

• Infrared radiation is felt as heat and causes skin to burn.

• Visible light from a laser which is very intense can damage the retina at the back of the eye.

• Ultraviolet can damage skin cells and lead to skin cancer and damage the eyes, it can cause skin to age prematurely.

• X-rays damage cells inside the body. They cause dangerous ionisation and when this happens with molecules in living cells, the genetic material of a cell, the DNA is damaged. This can lead to cancer. This is why doctors and dentists stand behind protective screens when taking lots of X-rays.

• Gamma rays also damage cells inside the body causing dangerous ionisation in living cells which damages DNA. This can lead to cell death and cancer.

What is ionising radiation?

Ultraviolet waves, X-rays and gamma rays are types of ionising radiation.

This means that they have enough energy to knock electrons from the shells of atoms, turning them into ions.

This process of ionisation can damage DNA in cells, leading to mutations in cells, which, in turn, can lead to cancer.

Ultraviolet radiation and suntan

Ultraviolet radiation, UV, is found naturally in sunlight.

We cannot see or feel ultraviolet radiation, but our skin responds to UV exposure by turning darker over time.

This is called a sun tan.

This is important, because prolonged exposure to ultraviolet radiation can cause skin cancer and damage to eyes.

It is sensible to wear high protection, UV blocking sunscreen on sunny days to avoid skin cancer.

Overexposure of our eyes to ultraviolet radiation can cause blindness, so we should also wear hats and sunglasses on sunny days.

It is worth remembering:

• Reflections from snow, sand and concrete increases the intensity of UV radiation.

• A light cloud cover does not block UV from the sun, and can still reach your skin.

• Water reflects only a small amount of UV. The rest can penetrate below the water's surface, and so you are not safe from UV in the sea.

The following practices are recommended to minimise UV exposure when outdoors:

• Avoid midday sun (10:00 a.m. - 3:00 p.m.).

• Wear clothing that is tightly woven to block sunlight.

• Wear a broad-brimmed hat that will shade your face, neck, and ears.

• Apply waterproof sunscreen - Factor 30 or higher, to all sun exposed skin – don’t forget your ears and nose.

• Wear UV protection sunglasses.

Microwaves are used for cooking food in microwave ovens.

Microwaves are easily absorbed by water molecules in food, causing them to vibrate more vigorously.

The microwave energy is changed to heat energy as it is absorbed, which cooks the food.

That's why foods that are high in water content, like fresh vegetables, can be cooked more quickly in microwave ovens.

Mobile phones work by sending and receiving low powered radio waves.

The radio waves are sent to, and received from, a mast or aerial, called a mobile phone base station.

The base station passes the signal/call into the landline network or on to the mast nearest the mobile phone the call is being made to.

Each mobile phone base station covers an area known as a cell.

Cells are aligned next to each other in a similar pattern to a honeycomb, and it is for this reason that mobile phone networks are sometimes referred to as cellular networks.

The phone masts can act as repeater stations, passing the call from mobile phone A to mobile phone B.

Base station transmitters/receivers are often positioned high up, often on tall radio masts.

They cannot be spaced so far apart that hills, tall buildings or the curvature of the Earth stop the beam.

What are the possible health risks of mobile phone use?

Mobile phones have only been in widespread use for a comparatively short time, so there is not much data about the possible long-term dangers of using them.

The phone is held close to the user’s head so the radio waves may have a small heating effect on the brain.

One of the few known effects of radio waves on the human body is a very small rise in temperature of up to 0.2^oC.

Do mobile phones cause cancer?

As of 2026, according to Cancer Research UK, the best scientific evidence shows that using mobile phones does not increase the risk of cancer.

The radio waves that mobile phones or phone masts transmit and receive is non-ionising and is very weak.

This non-ionising radiation does not have enough energy to damage DNA and cannot directly cause cancer.

But research is still continuing, to make sure there aren’t any potential long-term effects.

Concerns have been raised that exposure to radio waves from mobile phones might cause various health problems, ranging from brain tumours, cancer and infertility to headaches, sickness and memory loss.

So far, studies have not found that users have suffered any serious ill effects.

Microwaves are used to send signals to and from satellites.

The satellites can relay signals around the Earth.

Microwaves are used because they can pass through the Earth’s atmosphere and can travel through the vacuum of space.

The signals may be for television programmes, long distance telephone conversations, weather forecasting or spying.

Radio waves are not used to send signals to satellites as they are reflected by the Earth’s atmosphere and do not penetrate out into space and so would not reach the satellite.