1/6/09

Post date: Jan 06, 2009 2:41:28 AM

Bell Activity:

• Light, like sound, moves at a different speed for different materials.

• • The highest speed for light (or anything else in the universe) is about 300,000,000 meters per second or 186,000 miles per second. This occurs when light is moving through a vacuum (an area where there is no matter).

  • For light moving through other materials (such as glass, clear plastic, water, air, etc.) the speed of light is somewhat less.

  • We express the different speed of light with a ratio, called the "index of refraction"

    • • index of refraction = (speed of light in a vacuum) / (speed of light in the material)

      • can also write as n = c / v

      • For example, for a material where light moves at 150,000,000 m/s, the index of refraction is (300,000,000 m/s) / (150,000,000 m/s) = 2 = n

• • Changing speed of light

    • When light moves to a material with a different speed of light, the light will reflect, refract, or both

      • Law of reflection: The angle of incidence = the angle of reflection

      • Refraction

        • Light changes speed

        • Light bends at the surface

          • Think about rollerblading into grass at an angle, so your right foot goes into the grass first. Your left foot continues at the faster speed for a moment, so your left foot is moving faster than your right and you curve to the right.

        • The amount that light is bent can be calculated using Snell's law, which says that if light is moving from material 1 to material 2, and then the first index of refraction times the sine of the incident angle is equal to the second index of refraction times the sine of the refracted angle. This is written more succinctly as

• Index of refraction lab

  • • Calculate the index of refraction for a piece of glass (provided)

    • Work in groups of 3-4

    • Remember to measure angles from the normal line!

    • Due Wednesday

• • Page 354: 1-6 due Wednesday (attach to index of refraction lab)