Bending Light – Bending laser light with water

Bending laser light with water

Bending light experiment is a great demonstration for physics students. It is demonstrating total internal reflection of light in water.

Materials you will need to bend light with water:

  • laser pointer
  • stand for laser pointer
  • rubber band
  • clear empty soda bottle with cap
  • water
  • milk
  • permanent marker
  • metal skewer
  • flame
  • masking tape
  • sink

How to Bend Laser Light

  1. Fill the bottle with water and put a few drops of milk in to make it slightly cloudy. You can also try mixing in a little powdered milk or corn starch.
  2. Wrap the rubber band around the laser pointer so it is pressing the “on” button continuously.
  3. Set up the laser pointer so it is laying horizontally about 3 or 4 inches from the surface of the counter. Put it next to the bottle and adjust until you see the line of light passing through the milky water.
  4. With the marker, make a dot where the light beam touches the far side of the bottle. Pour out all the water.
  5. Heat the metal skewer in the flame until it is very hot. Use the tip to melt a small hole in the soda bottle at the dot.
  6. Cover the hole with a piece of masking tape. Put the cap on tight.
  7. Fill the bottle again with milky water. Place it on the counter next to the sink. Set up the laser pointer so it is aimed through the bottle at the hole. Take the tape off to see if the light hits the hole. (The water won’t come out until you loosen the cap — try it!)
  8. When everything’s arranged, loosen the cap until you get a stream of water pouring into the sink. Adjust the light or walk around the bottle until you can see the light in the curved stream of water.

    Why does light bend?

    The laser beam is “trapped” inside the water because of total internal reflection. As the light tries to pass from the more-dense water to the less-dense air, it bends. (This is called refraction.) At a certain point the light bends so much that it is bounces off the surface of the water. (This is called reflection.) In the narrow column of water, the light wave continues bouncing off the boundaries of the stream of water but cannot pass through into the air.

    bending laser light

    Bending light Optical cables

    The same principle applies with a piece of glass or plastic fibre optic cable.

Bending Light – Bending laser light with water on 2015-07-15 rated 4.9 of 5

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