Uses of Electromagnetic Waves

The electromagnetic spectrum is not just a list to memorise — each part of it does an enormous amount of work in everyday life. Radio waves carry television and radio across the country; microwaves cook your food and bounce signals off satellites; infrared warms you and carries internet traffic down optical fibres; visible light lets you see and take photographs; ultraviolet powers fluorescent lamps and reveals security marks; X-rays show the bones inside you; and gamma rays sterilise hospital equipment and treat cancer. The clever part is that each use depends on a property of that particular type of wave. This lesson, part of Topic P5 (Waves in matter) of OCR Gateway Science A, works through the main use of each group and explains why each band is suited to its job.

By the end of this lesson you should be able to state the main uses of radio, microwave, infrared, visible, ultraviolet, X-ray and gamma waves, and explain how the properties of each type of wave make it suitable for those uses.

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Linking Properties to Uses

Before going band by band, it helps to see the pattern: a wave's uses follow from its properties. Low-frequency waves (radio, microwave) penetrate the atmosphere and travel long distances, so they are used for communication. Infrared is readily absorbed and emitted by warm objects, so it is used for heating and thermal imaging. High-frequency waves (X-rays, gamma) carry a lot of energy and can penetrate the body, so they are used in medicine — but the same high energy makes them hazardous (covered in the next lesson). For every use below, try to name the property that makes the wave fit for the job.

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Radio Waves: Broadcasting and Communications

Radio waves — the longest-wavelength, lowest-frequency EM waves — are used mainly for communication: broadcasting television and radio programmes, and other long-range communications.

Why radio waves? They have long wavelengths that allow them to travel long distances, diffract (spread) around obstacles such as hills and buildings, and some are reflected by a layer of the atmosphere (the ionosphere) so they can reach receivers beyond the horizon. They also pass easily through the air without being strongly absorbed. A transmitter sends the radio waves out; an aerial (antenna) on your television or radio absorbs them and turns them back into an electrical signal. This makes radio waves ideal for sending signals from a broadcasting station to homes over a wide area.

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Microwaves: Cooking and Satellite Communications

Microwaves have two main uses: cooking food and satellite communications.

Cooking. In a microwave oven, the microwaves are absorbed by water molecules in the food. The absorbed energy makes the water molecules vibrate faster, which heats the food throughout — not just at the surface, but to a depth of a few centimetres where the microwaves penetrate. This cooks food quickly and from within.

Satellite communications. Microwaves used for communicating with satellites have the special property that they can pass through the Earth's atmosphere (including clouds) without being strongly absorbed. A signal is sent up from a transmitter on the ground, received by a satellite in orbit, and sent back down to a receiver elsewhere on Earth. This is how satellite TV, satellite phones and much long-distance communication work.

Exam Tip: Keep the two microwave uses distinct. Cooking works because microwaves are absorbed by water in the food and heat it. Satellite communication works because those microwaves pass through the atmosphere to reach the satellite. They are different microwave frequencies chosen for opposite reasons.

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Infrared: Heating, Remote Controls, Thermal Imaging and Optical Fibres

Infrared (IR) radiation has several important uses, all linked to the fact that it is strongly absorbed and emitted by objects and carries heat energy:

• Heating. Infrared is given out by anything hot — grills, toasters, electric heaters, radiant heaters. The infrared is absorbed by the food or the object, transferring energy and warming it. This is why you feel the warmth of a fire or a heat lamp.
• Remote controls. TV and other remote controls send short pulses of infrared to the appliance, which detects them and responds. Infrared is convenient here because it is invisible and works over the short range of a room.
• Thermal imaging. All objects emit infrared, and hotter objects emit more. A thermal imaging camera detects the infrared emitted by objects and turns it into a picture showing how hot each part is. This is used to find people in smoke or darkness, to spot heat loss from buildings, and in night-vision equipment.
• Optical fibres. Infrared (and visible light) is sent down thin glass optical fibres to carry data at high speed for the internet, telephone and cable TV. The infrared travels along the fibre by repeated reflection, carrying huge amounts of information very quickly over long distances with little energy loss.

Exam Tip: Infrared is the "heat radiation" band. Remember that all objects emit infrared, and hotter objects emit more — this is the basis of thermal imaging. Infrared (and visible light) is also what travels down optical fibres to carry data.

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Visible Light: Vision, Photography and Illumination

Visible light is the only part of the spectrum our eyes can detect, so its obvious use is vision — seeing the world around us. It also has technological uses:

• Photography. Cameras use visible light: light from a scene is focused by a lens onto a sensor (or film) to record an image.
• Illumination. Lamps and bulbs produce visible light to light up rooms, streets and screens so we can see.
• Visible light is also used (along with infrared) in optical fibres for fast data transmission.

Visible light is useful for these jobs because it is the radiation our eyes are sensitive to, and it can be focused and detected easily.

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Ultraviolet: Fluorescent Lamps, Security Marking and Tanning

Ultraviolet (UV) has a higher frequency (and energy) than visible light, and its uses make use of its ability to cause fluorescence and to affect the skin:

• Fluorescent lamps and tubes. Inside an energy-efficient fluorescent lamp, an electrical discharge produces ultraviolet, which strikes a coating of fluorescent chemical on the inside of the tube. The coating absorbs the UV and re-emits the energy as visible light, lighting the room. Energy-saving lamps work this way.
• Security marking. Special inks that are invisible in ordinary light but glow (fluoresce) under ultraviolet are used to mark valuables and bank notes. Shining a UV lamp on them reveals the hidden mark, helping to prevent theft and forgery.
• Tanning. Ultraviolet from the Sun (or from sun-beds) causes the skin to produce more pigment, giving a tan. (As the next lesson explains, UV also damages skin, so this use carries real risks.)

Exam Tip: The link to remember for UV is fluorescence — UV is absorbed by certain chemicals which then re-emit visible light. This single idea explains both fluorescent lamps (UV → visible light to see by) and security marking (hidden ink glows under UV).

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X-rays: Medical and Dental Imaging, and Security

X-rays have a very high frequency and energy, which lets them penetrate soft tissue but be absorbed by denser materials like bone and metal. This makes them ideal for seeing inside things: