PHYSICS LAB on SNELL's LAW

PHYSICS LAB on SNELL'S LAW

PURPOSE

To use a mathematical model (Snell’s law) to:

(1) determine the index of refraction of water.

(2) PREDICTTESTthe path of a ray of light through different plexiglass shapes.

PROCEDURE

The Index of Refraction of Water

1.Draw a horizontal line in the center of a white sheet of paper.

2.Place a dot in the center of this line.

3.Draw a normal to the line through this dot. Your normal should be a dashed line.

4.Draw rays that represent angles of incidence of 15°, 25°, 35°, and 45° with the normal : these will represent the angles of incidence in water. LOOK at the diagram now to be certain that you understand.

5.Place the semi-circular water tray so that its flat side is on the line.

normal line should be aligned with center dot.

.

Diagram of Set-up:

6.Carefully fill the tray about 2/3's full of water from the beakers provided.

7.Now it's laser pen time! Shine the laser through the curved side of the tray so that the beam can be seen directly above the incident paths you drew.

8.Have your partner mark a few dots on the refracted path of the light in air. You may need to do the "laser wiggle" to see the refracted path.

9.Remove the water tray and connect the dots, drawing out the path of light.

10.Measure the angle of refraction with respect to the normal (upon exiting the water). For each of the incident angles. The angle of refraction is after it passes the boundary, going from water into air.

11.Use your data to determine the index of refraction for water. Assume that the index for air is 1.00 and that light is passing from water into air. You're solving for nI!

12.Record your data and calculations in the table below.

DATA/CALCS

Follow Up Questions:

1. Describe & Explain what happens (a) when angle i = 0°, (b) when i = 55°.
2. Why, in step 7, does the light not change direction when it enters the curved side of the water tray?

1. Now use Snell's Law to PREDICT the path of a ray of light both into and out of the plexiglass shapes that are attached. You will need to use Snell’s law. These shapes are drawn to their actual size. (Remember, nair = 1.00 and nglass = 1.52)
2. Using a protractor and ruler, DRAWyour predicted path through each shape. Remember that the angles you've predicted are drawn between the ray of light and the normal to each boundary.
3. As you finish each of the 4 cases, TEST your prediction! The tests can be done at your table using the appropriate shapes (available from Mr. E. ) and your trusty laser pen.

Case 1

Case 2

Case 3

Case 4