• Question: I drew an arrow on a piece of paper and I then put a drinking glass infront of it. I poured some water into the glass and the arrow turned the other way. I think it acts as a lense but why is this?

    Asked by friartrout to Adam, Catherine, Karen, Leila, Nazim on 15 Mar 2012.
    • Photo: Adam Stevens

      Adam Stevens answered on 15 Mar 2012:

      Really hard to explain without a diagram. I might try and draw one!
      ___________________________________
      10 mins later….
      ___________________________________

      So I actually had to go and do this experiment to work out what you meant (I thought you meant the arrow was vertical and turned upside down).

      Anyway, here’s my diagram. I hope it helps!

      (P.S. Excellent question! Science in action!)

    • Photo: Karen Masters

      Karen Masters answered on 16 Mar 2012:

      Light which passes into (and out of) the water gets it’s direction changed – it’s called refraction. This is what causes the effect. It’s a good one. 🙂

    • Photo: Leila Battison

      Leila Battison answered on 19 Mar 2012:

      Its refraction that bends the light and the image of the arrow, so that by the time it has passed through the glass and out again, it has flipped around. You get refraction because light, like any wave, will travel faster in the water, and if it hits the glass at an angle, the light will change direction. This is enough to swap the direction of the arrow by the time the light has been through a couple of times.

      One of my favourite artists, M. C. Escher used refraction of light a lot in his paintings and drawings:

    • Photo: Nazim Bharmal

      Nazim Bharmal answered on 20 Mar 2012:

      The water in the glass causes a lens effect: because the glass is round, the light that passes through the outside of the glass travels through less water than the light through the middle. And the speed of light is less in water than in air. So that “flips” round the direction of the light, making it seem reversed to your eyes.

      To prove that it is the roundness of the glass, you can look down through the (flat) bottom and you don’t get the same effect.

      So that is proof at home that you can slow down light, just by sending it through water from a tap!

      (I did the experiment too! Although I used a newspaper and it only worked at the edge of the glass for me.)

Comments