Light, Sound and Waves

You can't see your face in the newspaper - but the writing is clear

Physics Narrative for 11-14 Supporting Physics Teaching

Reflection from a newspaper

At first sight, it may seem a little odd that although you can't see your face in the newspaper, as you can see the surface of the newspaper perfectly clearly and are able to pick out and read all of the print.

This is explained by the idea of diffuse reflection. Plenty of light is reflected from the newspaper, but it is jumbled – the surface is not smooth and shiny, so light coming in from one direction heads off in all directions (just like the lake).

If you wanted to model this process: rays strike each and every point on the surface at every possible angle and all of these rays are reflected such that the angle of incidence equals the angle of reflection. Plenty of light leaves the surface, but not in an orderly fashion. So you can see by the light leaving the newsprint – lots from a white spot on the page, not much from a black spot (colour papers in the next episode!)

Of course, we see everything around us in this way. Ray diagrams are intended to make things look simple by selecting key rays to model what beams will do. What is actually happening here is that countless beams are striking the surface of the newspaper every-which-way, being reflected every-which-way (that's why you can see the newspaper from many angles) and the eye picks up just some of those reflected rays. Which rays depends on the angle that you look at the paper from.

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