Page 20 - Curriculum Visions Dynamic Book

(Below) When light approaches glass, it may penetrate the glass or be reflected from its surface. If the light penetrates the glass, its angle of travel is changed. Not all light emerges from the glass. Some is absorbed and changed into heat.
Optical properties
When a beam of light falls on a piece of glass, some of the light is reflected from the glass surface, some of the light goes through the glass, and some is absorbed in the glass.
When light goes through glass, it is bent.
That is called refraction. The angle of refraction depends on the chemical composition of the glass. When the angle at which the light approaches (called the angle of incidence) is too steep, the so-called critical angle is reached, and after this the light is almost entirely reflected.
White light is a combination of the whole “rainbow” (spectrum) of visible colours. Each of
the colours in this rainbow has a slightly different wavelength. When white light enters glass, each colour in the light behaves differently. Each coloured light is bent differently. Blue light bends more sharply than red light in the same glass, and the colours in-between (green and yellow) are bent at angles between these extremes. The result is that the white light is split up into its spectrum of colours.
In a parallel-sided piece of glass these differences are not apparent because the bending that occurs when light enters the glass is balanced by the reverse bending as the light leaves the glass. However, when light enters a triangular glass block such as a prism, in which the sides are not parallel, the colours remain separated and show up as the spectrum.
Angle of incidence
Glass block
Angle of refraction
Mirror
Angle of incidence
Angle of reflection
Beam of white light
Red Orange Yellow Green Blue Indigo Violet
(Above) When a beam of white light enters a block of glass at an angle, the light is split up into its colours and emerges as bands of single-colour light – a spectrum.
20