Light as a Wave: Wavelength, Frequency and Amplitude

0:00Light travels as a wave. So how do we describe a wave of light?

0:06The dashed line through the middle is the rest line.

0:09Each highest point of the wave is a crest, and each lowest point is a trough.

0:16The wavelength is the length of one whole wave, from one crest to the next crest.

0:22The amplitude is the height of a crest above the rest line.

0:26Amplitude and wavelength are not the same. Wavelength is measured along the wave, and amplitude is measured up from the rest line.

0:36Frequency is the number of waves that pass a fixed point each second. Here it is slowed right down.

0:46Frequency is measured in hertz. One hertz means one wave per second.

0:52For light, the wavelength sets the colour. This red light has a wavelength of about 700 nanometres.

1:00A nanometre is one millionth of a millimetre.

1:04Violet light has a shorter wavelength, about 400 nanometres.

1:10In empty space, all colours of light travel at the same speed.

1:18More violet waves pass in the same time, so a shorter wavelength means a higher frequency.

1:25Real light has far more waves each second. Red light is about 430 trillion hertz, and violet light is about 750 trillion hertz.

1:36Amplitude sets the brightness. A bigger amplitude means brighter light of the same colour.

1:43Wavelength sets the colour of light, and amplitude sets its brightness.