Lights, Camera, REFRACTION!

water drop refraction Look at this drop of water, perched on a grass stalk (click to see a larger image). Within the water, a distorted image is present. This is caused by refraction of light coming from distant sources, being brought into focus by a lensing effect from the water drop. Refraction is present all the time, but just like reflection, our minds don’t process it well. When we look at something, there is the implicit expectation that the light that reaches our eyes travels in straight lines. The fact that it hasn’t in some cases, due to refraction, causes the optical illusions you see in the picture above and the movie below:

So what is it that causes this bending of light? Well, a better question to ask is what is  that is happening that causes the light to change direction? The answer to this question is that the speed of light is different in different materials, and it is this change in speed that causes the ray path deflection we call refraction. Look at the following diagram. As a vehicle encounters a grass verge at the side of a road, which scenario will happen? A, B or C?

axle refraction You all can see that it would be option A. As the right side wheel touches the grass, it loses traction, but the left side wheel maintains traction, cause a deflection to the right of the original trajectory. This link is to an excellent applet that allows you investigate how the metaphor of the car used to explain refraction above can be refined using Hughens concept of circular wavelets to demonstrate how this actually works with the wave model of light. Refraction can come into play in other circumstances as well. A common test problem refers to the archer fish, a fish which shoots a jet of water to knock insects into the water to be eaten. Here is a link to a youtube video that shows this phenomenon. Finally, you often see in Hollywood movies people shooting into water and the trajectory of the bullet changing. Here is a hi-speed camera movie that shows (in one scene) a bullet travelling through water. If you look carefully, you can see a slight change in direction.

Notes (part 5, part 6).

Explore posts in the same categories: Physics

4 Comments on “Lights, Camera, REFRACTION!”

  1. Mun Hon Says:


    I reckon that the picture of that water droplet looks cool. But techincally, I mean no offence, that person who voices that youtube video on this post sounds really annoying. It’s almost frustrating.

    Mun Hon, 10M

  2. mrgrichting Says:

    Hi Mun Hon,

    Yes, I found the accent to be a bit difficult as well, but the content is a nice simple introduction to the optical phenomena caused by refraction.

  3. […] things like reflection and refraction. I have previously written a post about this on this blog, here. However, in order to explain some more complicated phenomena, we need to use the Wave Model, which […]

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