Section 1 of 4Radio Waves and Microwaves
Long-wavelength waves are well suited to communication, while high-intensity microwaves heat food.
Broadcasting
- Radio waves are used for radio broadcasting and for communications such as air traffic control.
Mobile phones
- Mobile phone communication uses radio-frequency waves that pass through the air between phones and masts.
Cooking
- At very high intensities microwaves are used in microwave ovens to heat food quickly.
Why microwaves heat food
- Microwaves are absorbed by water molecules in food, which transfer their energy as thermal energy.
Section 2 of 4Infrared, Visible Light and Ultraviolet
Infrared, Visible Light and Ultraviolet
Infrared communication
- Infrared is used in fibre optic communications and in the infrared signals of TV remote controls.
Thermal imaging
- Warm objects emit infrared, which special thermal imaging cameras detect to show temperature differences.
Visible light
- Visible light is used for vision and photography, where it is focused onto a sensor or film to form an image.
Ultraviolet
- Ultraviolet is used in fluorescent lamps, because it makes some substances absorb it and glow as visible light.
Section 3 of 4X-rays and Gamma Rays
1
X-rays pass through soft body tissue but are absorbed by denser materials such as bone, which shows the skeleton on an image.
2
Medical X-rays are used to reveal the internal structure of patients, including the location of broken bones.
3
Gamma rays kill cells and bacteria, so they are used to sterilise medical equipment and some food.
4
Because gamma rays kill living cells, their use is carefully controlled in every application.
Section 4 of 4Exam Checklist & Tips
3.1.6 – Key Points for the Exam
- Fluorescence The process in which a substance absorbs ultraviolet light and re-emits it as visible light.
- Thermal imaging Creating an image from the infrared radiation emitted by warm objects.
- Fibre optic A thin glass or plastic fibre that carries light or infrared signals over long distances.
- Sterilisation Killing bacteria and other microorganisms, often using gamma rays on equipment.
Common Mistakes
- Saying that infrared is used to take X-ray images of bones; X-rays are used for that purpose.
- Forgetting that microwave ovens use high-intensity microwaves, which are absorbed mainly by water in the food.
- Confusing fluorescence with sunburn; sunburn is caused by ultraviolet damage to skin cells.
- Stating that radio waves are used to sterilise equipment; gamma rays are used for that purpose.