# AS AQA Phys Unit 1- Photons

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Electromagnetic waves

Light is just a small part of the spectrum of electromagnetic waves. Our eyes can only detect light and not the rest of the spectrum.

In a vacuum, all electromagnetic waves travel at the speed of light, c, which = 3.0*10^8ms^-1. Wavelength of electromagnetic radiation of frequency f in a vacuum is given by;

λ = c/f

Note; light wavelengths are often expressed in nanometres (nm), where 1nm = 0.000000001m = 10^-9m.

Main parts of the electromagnetic spectrum;

Type                          Wavelength Range

Microwave                    0.1m to 1mm

Infrared                         1mm to 700nm

Visible                           700nm to 400nm

Ultraviolet                      400nm to 1nm

X-rays                           <1nm

Gamma rays                 <1nm

An electromagnetic wave consists of an electric wave and a magnetic wave which travel together and vibrate;

• at right angles to each other and to the direction in which they are travelling.
• in phase with each other. The two waves reach a peak together so are in step, meaning…