Applications of Electromagnetic Waves

Microwaves are used for satellite communications. Signals travel from a ground station to a satellite, which can relay them to another ground station.

Higher Tier: microwaves can pass through Earth's atmosphere, so they can travel between the ground and a satellite rather than being reflected back towards Earth.

Microwaves and infrared: transferring energy to food

Microwaves are also used to cook food in microwave ovens.

Higher Tier: water in food absorbs microwaves strongly. Energy is transferred to the food, raising its temperature. The microwaves used for communication are not intended to produce this substantial heating effect.

Infrared radiation is used in electrical heaters and in cooking, such as grilling. The hot heating element emits infrared radiation, which transfers energy to the objects or food around it.

Higher Tier: when the food or another object absorbs infrared radiation, its internal energy increases and its temperature can rise. This makes infrared useful when the aim is heating rather than transmitting information.

Infrared cameras: detecting warm objects

Infrared cameras detect infrared radiation rather than relying on visible light. They produce thermal images that reveal temperature differences. For example, they can help locate a person in darkness.

Higher Tier: warm objects emit infrared radiation. An infrared camera detects this emission and represents differences using shades or colours. Those displayed colours are a way of showing the infrared information; they are not necessarily the objects' actual visible colours.

Visible light: communication along fibres

Visible light can carry information through fibre optic cables. Light signals travel along thin transparent fibres, allowing information to be sent from one end to the other.

Higher Tier: light can undergo total internal reflection at the fibre's boundary. Instead of escaping through the sides, it is repeatedly reflected back into the fibre and guided along it. This allows the signal to follow the cable's route.

Ultraviolet: lamps and tanning

Ultraviolet radiation is used in energy-efficient fluorescent lamps. Ultraviolet produced inside the lamp is absorbed by a fluorescent coating, which emits visible light. This conversion is called fluorescence.

Higher Tier: ultraviolet is suitable because it makes the coating fluoresce, producing the visible light needed for illumination. The useful output of the lamp is visible light, not ultraviolet.

Ultraviolet also causes sun tanning. Exposure stimulates the skin to produce more protective pigment, making it darker.

Higher Tier: ultraviolet produces this response in the skin, which is why it is used in tanning equipment. A tan does not mean that exposure is harmless: ultraviolet can damage skin and increase skin cancer risk.

X-rays and gamma rays: imaging and treatment

X-rays are used for medical imaging, particularly to examine bones. An X-ray detector records the radiation that passes through the body.

Higher Tier: X-rays pass through soft tissue more readily than through bone. Bone absorbs more of the radiation, so fewer X-rays reach the detector behind it. This difference produces contrast in the image and allows a fracture to be seen.

Gamma rays are used to treat cancer. Radiation is directed at the cancerous tissue to kill cancer cells.

Higher Tier: gamma rays can penetrate into the body and damage or kill cells. Their cell-killing effect makes them useful for treatment, but healthy tissue must also be protected as far as possible. The useful effect here is destroying cells, whereas the useful effect in X-ray imaging is producing an image from differences in absorption.

Suitability — Higher Tier

• Radio: some waves are reflected by the upper atmosphere, enabling long-range communication.
• Microwave: passes through the atmosphere for satellite links; absorbed by water in food for heating.
• Infrared: absorption transfers energy for heating; emission from warm objects enables thermal imaging.
• Visible light: total internal reflection guides signals along optical fibres.
• Ultraviolet: causes fluorescent coatings to emit visible light; stimulates tanning in skin.
• X-ray: soft tissue transmits more than bone, producing image contrast.
• Gamma ray: penetrates tissue and kills cells, allowing cancer treatment.