Light can differ in intensity and wavelength

Knowing that light travels in straight lines tells us very little about what light is. Using the definition that energy is something that gives an object the capability to do something to something else then we can safely say that light is a form of energy. It is also safe to say that even though we know that light is a form of energy we still have only vague ideas on what it is. Some scientists believe that light can be described as waves of energy (electromagnetic waves) based upon the ideas of James Clerk Maxwell (1831-1879) while other believe that light has a particle or corpuscle like structure consisting of discreet packages of energy.

Both of these descriptions are models of what we think light is. Like any good model it has to be able to describe the real thing and also how the real thing behaves and in this case both models work quite well.

The wave model is one which we will focus on here. If we think of light as an oscillating wave of energy then we can represent it on paper in the following way (a model of a model!). In the diagram below there are two waves both of the same wavelength but with different amplitudes.

What significance does the amplitude of the wave have? The amplitude of a wave tells us about the intensity or brightness of the light relative to other light waves of the same wavelength. Both Wave 1 and Wave 2 have the same wavelength but different amplitudes.

The wavelength of light is an important property for it is this that determines the nature of the light. Red light has a different wavelength to that of blue light and green light has a different wavelength from both of them. In the spectrum of light that we are familiar with violet has the shortest wavelength while red has the longest.

Radio waves, X-rays, Ultra violet light, infra red and radar can all be described (modelled) like light as waves and they all have their own characteristic wavelengths and form what is known as the electromagnetic spectrum.

Contents

Light does appear to travel in straight lines
The distinction between reflection and scattering, How images are formed in a mirror
The colour of an object depends on the wavelength of light that it scatters
Objects are seen when light enters the eye through the pupil
Self assessment