The electromagnetic spectrum: dispersion, regions, properties, uses

Last time

Before we start: last time, in Critical angle and total internal reflection, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

A whole family of waves

Light from a lamp, the signal from a phone mast, the X-ray at the hospital. They look nothing alike, yet they are the same kind of wave. All are electromagnetic waves, and all travel at the same speed through space. The only difference is their frequency.

Dispersion

White light is a mixture of colours. A glass prism splits it into a band of colours called a spectrum. The splitting is called dispersion. It happens because each colour is refracted by a different amount. The order: red, orange, yellow, green, blue, indigo, violet. Red bends least and violet bends most.

The visible spectrum

Red light has the lowest frequency and the longest wavelength of the visible colours. Violet has the highest frequency and the shortest wavelength. All the colours travel at the same speed in a vacuum. In glass the violet is slowest, which is why it bends most.

The spectrum

From lowest frequency to highest. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Going this way, the frequency increases and the wavelength decreases. Radio waves can be a kilometre long. Gamma rays are smaller than an atom.

Shared properties

All electromagnetic waves are transverse waves. All travel through a vacuum, which is how sunlight reaches the Earth. All travel at the same speed in a vacuum, 3.0 times 10 to the 8 metres per second. They can be reflected, refracted and diffracted.