Light, Sound and Waves

Reflection of light at home

Physics Narrative for 11-14 Supporting Physics Teaching

Paint and reflections

Surfaces are made to be reflective in different ways to create different moods.

DIY shops sell different kinds of paint which are designed to provide contrasting effects not only in terms of colour but also in the ways in which light is reflected from the surface. The two extremes of finish are gloss and matt, with satin in between. What different effects do these paints produce and how are they achieved?

With gloss paint the particles at the surface of the paint are very small and when the paint dries they end up forming what is in effect a very flat, plane surface which acts just like a mirror. Any light shining onto this surface is reflected regularly and it may be possible to see the image of an object (your face!) as light is reflected.

At a microscopic level the surface of matt paint, when it dries, is very uneven. An analogy is that when magnified it resembles a pebbled beach. Here the light from a luminous source will hit each pebble and whilst each small part of each pebble will reflect light according to the laws of reflection, the overall effect is that the light is scattered in all directions. Our eyes gather light from parts of many different pebbles as diffuse reflection occurs, making the matt finish appear dull in comparison with the gloss surface.

is formalised by Law of Reflection
can be exhibited by Progressive Wave
has the special case Total Internal Reflection
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