08. AWKWARD QUESTION AND ANSWER

Here’s a reminder of the question:

Little Jimmy is an intelligent five-year old who loves jumping in and out of puddles. His mother, however, does not like little Jimmy getting his clothes wet. Little Jimmy has decided that when he grows up he is going to be a scientist. His first task, he decides, will be to stop wet clothes from looking darker. That way his mum will never know his trousers are wet and he can splash in and out of puddles all day long. Of course, this is impossible, but just why do things appear darker when wet?

Are you ready for the answer?

We see objects because light is reflected (or emitted) by them and the light then enters our eyes. (Sounds obvious, but ancient philosophers reckoned it was the other way round). The more light that enters our eyes from an object, the brighter it appears, so less light must be reflected from wet objects which therefore makes them look darker. So the simple answer to our question is ‘because they reflect less light’.

Connoisseurs of Planet Science AQs would most likely then ask why exactly should wet objects reflect less light. The answer to this lies in the behaviour of rays of light when they hit the surface of little Jimmy’s wet clothes. Some of the light that hits the watery layer will pass into the water and its direction will change because of refraction. (We met refraction recently with Arty Pooper’s beach party AQ — only this time it was travelling sound rather than light). These rays of light can then have different alternative fates to those they would have had with dry fabric. The rays may ultimately be reflected back from the clothes but in directions that don’t make the eye of an observer. Or they may be ‘conducted’ deeper into the fabric in the layer of water surrounding clothing fibres, in a manner similar to light travelling down optic fibres. This increases the chance that rays will be absorbed by the fabric rather than reflected away from the fabric into an observer’s eyes. So, in a shell made of nut, refraction of light in the water layer around the fibres ‘robs’ the eye of some of the light that would have entered had the fabric been dry. Less light entering the eye means the fabric looks darker.

>>>>>>>>>>>>>>>>>>>

Moving on to this week’s Awkward Question, the second question as sent in by Elizabeth Hayden. Apparently it has been bothering her for years so let’s put her out of her misery:

Why does even the sweetest pure orange juice taste so foul just after you've brushed your teeth?

Answer next week.