Refraction Through a Glass Plate
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Purpose
The purpose of this lab is to measure the index of refraction of a glass plate, and the speed of light in the glass.
Apparatus
- cardboard
- 4 pins
- straight edge
- glass plate
- piece of 8 1/2 by 11 paper
Procedure
- Secure the card board on the lab table.
- Lay the 8 1/2 by 11 paper directly on the card board.
- Hold the glass plate up to the light so that you can look through the smallest dimension(height) at the light. You will be able to see through it as you look in one direction but not if you rotate it ninety degrees.
- Place the glass plate on the paper in such a way that you can easily see through the plate as discussed in #3 above.
- Trace around the glass plate with your pencil.
- Place 2 pins in the paper and cardboard on the far side of the glass plate. Place pin A next to the plate approximately 3/4 inch from the left side. Place pin B about 1 inch further away from theplate and also approximately 1/4 inch to the left of pin A.
- With your eyes level with the flat glass plate, look at the pins through the glass plate. Place Pin C as close as possible to the near side of glass plate so that pin A, B and C appear to be in a straight line as you view A and B through the glass plate and C in front of the plate.
- Now place pin D also an inch or so from the plate on the same side as Pin C so that ABCD appear to be a straight line. Remember to view pins A and B through the glass plate as in step 7.
- Be sure that the pin holes are deep enough so that you can easily see them after the pins are removed.
- Put the pins back in the container and remove the glass plate from the paper. Using a straight edge and pencil, draw line segments AB, BC and CD.
- Using a protractor, measure the angle of incidence and angle of refraction the light entering and exiting the glass.
- The index of refraction of the glass gives an indication of the optical density of the glass. Using Snell's law below, calculate the index of refraction of the glass.
- The index of refraction of the glass is also the ratio of the speed of light in air to the speed of light in the glass. Find the speed of light in the glass.
