# The Electromagnetic Spectrum

The electromagnetic spectrum displays all of he forms radiation arranged
from shortest to longest wavelength. All of the waves in the spectrum
travel at the speed of light which is approximately 3 x 10^{8} ms^{-1}.

Typical wavelengths

For the exam it is vital you know the order, the range of wavelengths and a typical value for each.

**Photons**

Light can be referred to as either a wave or as a particle called a photon.
A Photon is defined as a quantum of energy. The properties of waves (frequency
in this case) can be combined with a particle like nature in the following
equation:

Photon energy (J) = hf

Where f = Frequency (Hz)

h = Planks constant = 6.63 x 10^{-34} Js (This given in the exam)

Here the energy of a photon has been combined with the frequency of a wave. This is sometimes referred to as wave-particle duality.

### Electronvolts

Because the energies of individual photons are so small the electronvolt is sometimes more useful.

**Definition**

One eletronvolt is defined as the energy transferred when an electron
moves between two points separated by a potential difference of one volt.

The electronvolt can be calculated from Joules using the following conversion:

1.6 x 10^{-19} J = 1 eV

Alternatively 1 Electron carries 1.6 x 10^{-19} Coulombs of charge.

This conversion factor is also given in the exam paper. However, it must
be noted that the electronvolt is not an SI unit of energy and therefore
for any calculations involving the electronvolt you must first convert
it into joules.