Electromagnetic Spectrum
The electromagnetic (em) spectrum is light in all its wavelengths. This is from very short wavelength, gamma radiation, λ < 10 × 10-12 m to the very long wavelength, AM radio waves, λ > 3 × 102 m. The enourmous range of over 14 orders of magnitude is split up into smaller sections dependent on the wavelength of the light.
All electromagnetic waves travel at the speed of light, 3 .0 × 108 m/s because they are all light waves. These waves are able to travel through a vacuum without the need for any propogating material. The waves are all transverse waves where the oscillation of the wave is at 90° to the direction of energy transfer of the wave.
Wavelength and frequency range
| Part of Spectrum | Key Wavelength (m) | Key Frequency (Hz) |
|---|---|---|
| Radio & TV | Greater than 1 | Less than 3.0 × 108 |
| Microwave | 1 × 10-2 | 1 × 1010 |
| Infra-red | 1 × 10-5 | 1 × 1013 |
| Visible | 400 × 10-9 to 700 × 10-9 | 7.5 × 1014 to 4.3 × 1014 |
| Ultraviolet | 1 × 10-8 | 1 × 1016 |
| X-ray | 1 × 10-10 | 1 × 1018 |
| Gamma | 1 × 10-12 | 1 × 1020 |
Applications, Sources and Detection
| Part of Spectrum | Sources | Detectors | Applictions |
|---|---|---|---|
| Radio & TV | Electric circuits | Aerial | Signals for radio and TV, communications |
| Microwave | circuits and microwave ovens | Aerial | Communications with satellites and mobile phones as well as heating food rapidly |
| Infra-red | Electric circuits, hot or warm objects, the Sun | Heat sensitive paper, black bulb thermometers, electronic detector e.g. LDR, photodiode, thermistor | Security lighting detector, tv remote control |
| Visible | Lamps, LEDs, lasers, the Sun | the retina of the eye, photgraphic film, electronic sensors, LDRs | Sight, photography, fibre optics used in communications and Internet |
| Ultraviolet | The Sun, gas discharge lamps | Causes some materials to fluoresce (glow in the dark) | Sun-tan lamp, detecting UV inks in bank notes, killing bacteria in water treatment, making vitamin D |
| X-ray | Very high speed electrons hitting metal target | photographic film | imaging bones to check for breaks, customs checking of container contents |
| Gamma | decay of radioactive nuclei | photgraphic film, GM tube | killing cancer, medical tracer, sterilising medical equipment, hole detection in underground pipes, extending shelf life of strwaberries and other fruit |
