LIGHT Light is a form of energy that travels by electromagnetic waves.
Although light can also be viewed as ‘bundles of energy’ called photons, most of the phenomena of light are explained by describing light as a wave.
The question about the nature of light (whether it is wave or particle) stretches back to the seventeenth century, where it was debated by Sir Isaac Newton and Christiaan Huygens, amongst others.
Newton’s corpuscular theory of light
Newton believed that light was composed of corpuscles (bullet-like particles of matter), which were emitted in all directions from any source of light.
CHRISTIAAN HUYGENS, 1629–95 (DUTCH)
He proposed the wave nature of light, contradicting Newton’s corpuscular theory. He also worked with Blaise Pascal to develop the theories of mathematical probability.
Huygens’ wave theory of light Christiaan Huygens believed that light was a wave.
The two theories of light were in conflict The notion that light can be described as both wave and particle (wave-particle duality) was not given any consideration in the sevententh century. It was therefore up to someone to devise an experiment to settle the debate as to whether light is wave or particle. It took over a century for that to happen.
Young’s ‘Double Slit’ Experiment
The English physicist Thomas Young devised an experiment to show that light undergoes diffraction and displays interference, two phenomena that only waves demonstrate.
The experiment involves setting two coherent wave sources very close to each other. This was done by shining light onto a carbon-covered glass slide which had two narrow slits scratched onto it. The scratches acted at the light sources.
When a screen is placed in front of the double-slit, a series of bright and dark regions (called fringes) can be seen (Fig 14.1).The only explanation for this pattern is that light is made up of waves.When the light waves pass through the two gaps in the carbon-covered
