An otherwise straight beam of light...

SmarterThanThat Experiments

Sunday, 30 November 2008 00:37 Written by mooeypoo

All super-thieves know that lasers go straight. It’s the tenet of their masterplan to jump over, crawl under and squeeze between those annoying laser beams around whatever-it-is they are interested in stealing. It can take them weeks to study the angles and train to spray dust over it so they can see them. Talented thieves.

I wonder what would their world look like if they knew that light can be bent. Well, in huge distances (like space) light is bent with gravit, which is pretty cool, but it takes a big body of mass and quite a large distance to do that. I am not going to travel light years to see light bend. I’m going to do it in my own bathroom. You can too. In your own bathroom.

So what actually happens with light to cause it to “bend”? In short distances, light travels in straight lines, and if they are otherwise undisturbed, they will go on forever. Or at least for a really really really really long time. That’s how we see distant stars, their light travels huge distances and reaches our telescopes (or eyes, if the night is clear).

Using the principle of refraction, we can simulate a situation where a light beam is ‘bent’. Think about a bunch of mirrors, each refracting the light in a slight angle towards another mirror - eventually directing a beam of light at a completely different angle. That seems easy enough, and - unsurprisingly - that is exactly what is happening within the flow of water.

Materials Used in this Experiment

• A Plastic Bottle - preferably clear and empty.
• Duct Tape. (I used blue, you can use whichever color you feel like).
• Laser Pen, or other directed light source.
• Water.

Preparations

Take the plastic bottle and poke a hole in it with a pin. I recommend expanding it a bit, the hole in my bottle was about 2mm in radius. The trick is to create a large enough hole to encompase the entire laser beam, but not large enough to have the water just pour out uncontrollably. It took me about 3 attempts to get this straight. Err.. bent.

Now, cover the hole with the duct tape and poke another hole through the not-for-long sealed hole. The duct tape is not absolutely necessary, but it will help directing the laser ray towards the hole. You would be amazed how difficult it can be to aim when water is pouring out on top of you…

Seal the hole with your finger and fill the bottle with water. When it’s full, close the cap. The pressure inside the bottle will prevent the water from coming out through the hole - as long as you are careful not to squeeze the bottle. Or drop it. Or tilt it too fast…. okay, maybe you should keep your finger on the hole anyway.

Put the bottle somewhere wet (or that you wouldn’t mind getting wet, like a bath tub), turn your laser beam on and point it at the hole. Release the cap.

Water should be coming out now, and if you aim your laser light properly, they should refract the beam towards the surface and appear slightly reddish (or.. whatever color your laser beam is).

Real Life Applications

• Optic Cables: Spread over the ocean and land, optic cables direct light from one point to another using this principle. No, they are not made of water, they’re made of a matterial that is, actually, better refracting (light beams don’t ‘come out’ of the cable mid-way, usually, only at its ends). This means that the light does not lose energy along the way, and reaches the destination in the speed of light. Which is fast. Very fast. Yay for optic cables.

Resources

• Light Refraction: http://www.ps.missouri.edu/rickspage/refract/refraction.html
• Refraction of Light: http://sol.sci.uop.edu/~jfalward/refraction/refraction.html
• Full Bottle, Hole, No Leak: http://www.newton.dep.anl.gov/askasci/phy00/phy00946.htm
• Howtoons: http://www.instructables.com/id/Bending-Light/

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