3. Photons

Electromagnetic waves

In a vacuum, all electromagnetic waves travel at the speed of light, c, 3.00 x 10^8 m/s

Wavelength = c/f

Electromagnetic waves

• consists of an electric wave and a magnetic wave which travel together and vibrate
• At right angles to each other and to the direction they are travelling in
• in phase with each other

Photons

A photon is a short burst of electromagnetic waves.

The photon theory was used to explain the photoelectric effect. This is the emission of electricity from a metal surface when light is directed at the surface.

Photon energy - E=hf

h = Planck constant = 6.63 x 10^-34 Js

Laser power

the power of the beam = nhf

n = the number of photons in the beam that pass a fixed point each second