Section 1 of 4Radio and Microwaves
Broadcasting
- Radio waves carry radio and television signals, because they can be transmitted over long distances.
Short-range links
- Bluetooth uses radio waves to connect phones and speakers over short distances without cables.
Mobile networks
- Microwaves carry phone and satellite signals between transmitter masts and satellites.
Cooking
- Microwaves at a particular frequency are absorbed by water molecules, which heats food that contains water.
Section 2 of 4Infrared and Visible Light
Remote controls
- Small infrared LEDs send invisible pulses of infrared to a receiver on a television.
Thermal imaging
- Infrared cameras detect emitted radiation to show temperature differences in buildings or in medicine.
Fibre optics
- Infrared is transmitted along optical fibres with little loss, carrying large volumes of data.
Vision and cameras
- Visible light allows our eyes to see, and cameras record it as photographs and video.
Section 3 of 4Ultraviolet, X-rays and Gamma Rays
Ultraviolet, X-rays and Gamma Rays
Security markings
- Ultraviolet makes special inks fluoresce, so the markings on banknotes show only under UV light.
Sterilising
- Ultraviolet and gamma rays kill bacteria, so they are used to sterilise water, food and medical equipment.
Medical imaging
- X-rays pass through soft tissue but are absorbed by bone, so they show skeletons and teeth clearly.
Cancer treatment
- Carefully aimed gamma rays destroy cancerous cells, and the dose is limited to protect healthy tissue.
Section 4 of 4Exam Checklist & Tips
3.2.4 – Key Points for the Exam
- Fluorescence The process in which a substance absorbs ultraviolet and re-emits visible light.
- Fibre optic A thin glass or plastic fibre that carries light signals over long distances.
- Thermal imaging Producing a picture from the infrared radiation emitted by objects.
- Sterilisation The killing of bacteria and other microbes to make an object or substance safe.
- Contrast medium A substance taken into the body that absorbs X-rays, making organs visible on an image.
Common Mistakes
- Saying microwave ovens cook food by using infrared radiation.
- Saying ultraviolet security markings can be seen in ordinary light, when they only show under UV light.
- Claiming that radio waves are used for X-ray imaging.