P1bL1 Uses of Electromagnetic Radiation
Key Words
Electromagnetic radiation - radiation that behaves like light.
Gamma rays - very energetic (very short wave) electromagnetic radiation from nuclei.
Infra red radiation - radiation given out by warm objects with slightly longer wavelength than visible red light.
Microwaves - short wavelength radio waves, wave length of about 1 - 10 cm.
Radio waves - long wavelength electromagnetic radiation given out by high frequency alternating currents.
Rays - beams of radiation.
Spectrum - a family of waves where one kind of wave runs into another without a clear boundary.
Ultra-violet - short wavelength light, with wavelength slightly shorter than visible violet light.
Wave - a disturbance that carries energy from a source.
X-rays - short wavelength radiation less energetic than gamma rays, but more energetic than ultraviolet.
Grade E
Electromagnetic radiation carries energy in the form of electromagnetic waves. All EM radiation behaves like light:
- It travels in straight lines;
- It travels at 300 000 000 m/s in a vacuum;
- IT can be reflected and refracted.
The electromagnetic spectrum is a large family of waves which have a wavelength of 2000 m to 10-14 m. Here are some:
| Wave | Wavelength | Use | Energy |
| Radio waves | 2000 m to 10 cm | Radio and TV | Extremely low |
| Microwaves | 0.1 mm - 10 cm | Microwave ovens, digital communications | Very low |
| Infra red | 1 mm - 0.1 mm | Radiation of heat | Low |
| Light | 1 × 10-6 m | What we see with. | Moderate |
| Ultra violet | 1 × 10-7 m | Sun beds, counterfeit note detectors | High |
| X-rays | 1 × 10-7 m - 1 × 10-10 m | Shadow pictures of bones | Higher |
| Gamma rays | 1 × 10-11 m - 1 × 10-14 m | Killing cancer cells. | Very high |
There are no distinct boundaries between each type of wave. High energy UV rays can also be described as low energy X-rays.
Grade C
There are other uses of EM radiation:
| Wave | Use |
| Radio waves |
Radio waves used for broadcasting. TV waves have a wavelength of about 2 m. |
| Microwaves | Digital communications from satellites, radar speed traps |
| Infra red | Thermograms show up heat loss. Infra red detectors show up body heat |
| Light | Visible light comes from hot objects like the sun. |
| Ultra violet | UV light comes from very hot objects |
| X-rays | Shadow pictures of bones |
| Gamma rays | Detecting leaks in underground pipes |
EM Waves are transverse. This means that the particles vibrate at right angles to the direction of travel. A transverse wave looks like this:
Sound waves are longitudinal. This means that the particles of air vibrate parallel to the direction of travel. Here is a longitudinal wave:
The compressions are areas of high pressure, where the particles are squashed together. The rarefactions are areas of low pressure, where the particles are spread out.
Grade A
Security measures at airports use EM radiation, for example X rays are used to screen passengers' luggage. UV light tells immigration officials if passports have been forged.
Electromagnetic waves can be made by oscillating electric currents (currents that go forwards and backwards). The electrical waves made from a microphone and a TV camera are mixed in with a high frequency alternating current, which is passed through a wire at the transmitter.
The waves set up a similar (but tiny) oscillating current in the receiver (TV or radio). This is amplified to give the picture and sound.
