What is light?
Light is produced by the Sun, and by objects such as light bulbs and matches. Light carries energy and travels as a wave. Light travels at a speed of 300,000,000 metres per second, which is much faster than the speed of sound. Light waves travel in straight lines.
Light is a form of energy and can be changed from one form into another.
Light energy can be used to make other useful forms of energy. It can be converted into electrical energy in a solar cell or chemical energy in the leaves of plants.
Passing white light through a prism
Splitting white light
A prism棱镜 splits分散 a ray of white light into the colours of the rainbow. This process is known as dispersion色散.
Dispersion occurs because different colours of light refract differently. Red light refracts the least; violet light the most. The order of the colours in the spectrum is always the same. Use this phrase to remember the order of colours:
If there are water droplets in the air and the sun is illuminating them from behind, then you may see a rainbow in the air. Light enters the water droplets and refracts. It then reflects off the back of the rain drop.
The red light refracts the least and the violet the most. This causes dispersion of the sunlight.
The visible light spectrum
How do we see things?
An object that gives out light is described as luminous. How does light from a luminous object such as a light bulb reach the eye? Light travels in a straight line directly into the eye. An object that does not give out light is non-luminous. How does your eye see a non-luminous object such as a comb? Light hits the comb and some of it is reflected into the eye.
Seeing different colours
How do we see the different colours in this frog and lily? The frog’s red skin absorbs all of the colours except red and so it appears red.
The black skin absorbs all colours. No colours are reflected and so it appears black.
The lily’s centre absorbs all colours except red and green. It reflects red and green light, and so appears yellow. The leaves reflect all the colours and so appear white.
Using filters of primary colours
A filter absorbs some colours of white light and lets other colours through to create coloured light. A red filter absorbs all colours… …apart from red light. A blue filter absorbs all colours… …apart from blue light. A green filter absorbs all colours...
…apart from green light.
How do we see colours in coloured light?