3. What do mean by opaque, transparent and translucent materials?

In terms of visible light, materials may be opaque, transparent or translucent.

What are the difference between opaque, transparent and translucent materials?

Different objects (materials) may absorb, transmit or reflect different wavelengths of visible light in different ways - this makes explaining 'colour' a bit tricky at times!

Opaque means that visible light cannot be transmitted through the material. If the object does not transmit light then some colour wavelengths are absorbed (you don't see these) and other colours are reflected - the combination of these wavelengths make up the colour you see.

So, the colour of an opaque object depends on which colours in the visible light spectrum are the most strongly reflected and those most strongly absorbed.

Examples are described in the next sections e.g. a blue opaque object looks blue because all the other colours are absorbed and only blue wavelengths are reflected back into your eye.

Mixing colours is discussed in the next section.

Perfectly white objects reflect all the coloured wavelengths of the visible spectrum - white means you are seeing all or almost all the light that shone on the object - very little, if any, is absorbed by a shiny white surface.

Perfectly black objects absorb all the coloured wavelengths of the visible spectrum - black means you see little or none of the light that shone on the object - very little, if any, is reflected by a black matt surface.

Transparent materials will transmit all or a selection of visible light wavelengths through - not all the light that hits the surface is absorbed or reflected.

The observed colour of a transparent material depends on which wavelengths are transmitted.

e.g. 'colourless glass transmits most of the visible spectrum. Blue glass transmits 'blue' wavelengths and absorbs all the 'green to red' wavelengths. More examples are described in the next sections.

Translucent materials only allow a portion of the light through and some wavelengths may be reflected or absorbed.

You cannot see a clear image through a translucent material - tissue paper and frosted glass are good examples, and, can be a variety of colours.

For both transparent and translucent materials, their colour is determined by the colour wavelengths most strongly transmitted.