3.12 explain some of the uses of electromagnetic radiations, including: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays.

Radio waves: broadcasting and communications

• Broadcasting and communications -  The purpose of radio waves is to send information from one place to another without the use of wires. This can be done because radio waves have a very long wavelength that can be diffracted (bent) around the curved surface of the earth. Radio waves are emitted by a transmitter. Then radio waves are received by the antenna and converted to mechanical waves (by the speaker) which can be heard. This makes it possible for sound and TV signals to travel around the world.

Microwaves: cooking and satellite transmissions

• Heat up or cook food. This is because water molecules in food absorb certain wavelengths of microwaves and become really hot. 
• Satellite transmissions - Microwaves can pass easily through the Earth's atmosphere (radio waves can't do this). Therefore, they can also be used to send and receive information from the satellites. Phones use for communication; signals are sent to the satellite and then passed on to their destination. Wifi also uses microwaves.
• Speed cameras and radars (in boats and planes) - This consists of a burst of microwaves. When these waves hit objects, they create an echo. By using the time that it takes for echoes to come back, the distance from the object can be worked out.

Infrared: heaters and night vision equipment

• Heaters or heat lamps -  heaters transfer energy to a body with a lower temperature through radiation. The same idea is used in toasters and electric grills to cook. 
• Special Cameras (night vision equipment) - All objects including your body emit infrared radiation. The hotter the object, the more infrared radiation it will emit. Special cameras detect infrared radiation and create images without the need of visible light. This camera can be used to find bodies trapped in collapsed buildings, to follow criminals in dark areas and to check the heat released from different objects.
• Remote controllers - This is also used by remote controllers by emitting different types of infrared radiation patterns which send different commands to the appliance. This is used in TV and car locking systems. They are suitable for this use as they have a low penetrating power (only works for short distances) and doesn't interfere with other waves.

Visible light: optical fibres and photography

• Laser Readers Visible light in lasers can be used to read bar codes of the different items in a shop or in a computer to read and write in compact disks. 
• Photography - Cameras use the lens to focus visible onto a light-sensitive film or electronic sector. This then changes the different setting in the camera (like shutter speed and aperture) to capture the amount needed of visible light in a picture in different conditions. 
• Optical fibres - Visible light can also be used in optical fibres to carry light signals with very little loss of strength. Optical fibres carry coded information in the form of light signals. They are used to send computer data, telephone calls or transmit electrical signals.

Ultraviolet: fluorescent lamps

• Security and authenticity -  Ultraviolet light is part of the invisible light emitted by the sun. Security and to check the authenticity of various objects. Security markers contain chemicals that glow when exposed to UV light but are invisible in normal light. This can be used to send secret messages. Ultraviolet light is also used in bank notes (money) to detect forged notes. Original notes contain chemicals that glow when they are exposed to ultraviolet light. Forged notes don't contain these chemicals. 
• Fluorescent lamps - Fluorescent tubes also use ultraviolet light, they glow when the UV they produce (mercury vapour produces UV light when there is a current through it) strikes a special coating on the inside of the tube (fluorescent powder). This emits visible light.

X-Rays: observing the internal structure of objects and materials and medical applications

• Radiographs (check the patient's bones) - This is because X-Rays can pass through soft body tissue but not bones.
• Security - They are also used in airports for security to see what's inside a suitcase without having to open it. This helps security identify dangerous objects like guns or knives.
• Industry - With the use of X-Rays, people can check internal structures to looks for cracks in a building or faults in a piece of machinery.

Gamma rays: sterilising food and medical equipment and cancer treatment

• Sterilise food and medical equipment - this is because gamma rays have a tremendous amount of energy, this energy can kill microbes from food and medical equipment to avoid infections. 
• Treat Cancer - Large amounts of gamma rays can be used to treat cancer. They need to be directly targeted at the cancerous growth. Gamma rays work by damaging the body cells. Healthy cells can repair themselves from the damage caused, but cancerous cells can't and end up dying.