Glass

Why can we see through glass?

We can see through glass because it allows the light rays to pass through. Glass is a hard, brittle material made by fusing silica with the oxides of silicate of such metals as sodium, magnesium, calcium and potassium. The product is cooled rapidly to prevent the formation of any crystalline material which would interfere with the passage of light. The melting point of glass is about 800-950° Centigrade (1,472° Fahrenheit).

In fact, light does not travel straight through glass but it bent or refracted. The light is bent twice, first when it enters the glass and then back to its original direction, when it comes out at the other side. Every transparent material bends light, but the amount (described by a number called index of refraction) varies with the density of material, the greater is the amount of bending and the higher the index. The speed of light also varies as it enters another material becoming slower as the density of the material increases.

The ability of light to refract light rays has made possible the designing of the lenses which are essential for the important science of optics. A convex lens – a lens with one or both of its surfaces bulging outward – bends light rays inward. A concave lens – with one or both of its surfaces curving inward – spreads light rays outward.