# snells law lab

Materials: White paper, protractor, glass baking dish, metric ruler, and scientific calculator

Procedure: Read all steps of the procedure before you actually begin the lab activity.

Step 1: Place your square refraction plate (glass baking dish) in the center of your paper. Use your pencil to outline the refraction plate.

Step 2: Remove the glass plate from the paper. You will replace it in the next step. Draw a normal(labeled “N”) at the top left section of the outline. Notice that the normal is not drawn at the center of the plate. Draw an incident ray to the left of the normal.

Use your protractor to draw an angle of incidence of 30.0 degrees. Carefully measure the angle again to be sure it is 30.0 degrees.

Hint: Remember that the angle of incidence is formed by the incident ray and the normal, NOT the side of the refraction plate. This is where students often make an error.

Step 3: Now carefully replace the glass plate inside the tracing line you drew in step 2. Position the paper and glass plate about 10-15 cm from the edge of your table. Be sure that the glass plate is positioned inside the pencil outline.

Step 4: This step is tricky. Read this step very carefully. Get down on your knees and position your head so that your eyes are level with the glass plate. You want to be able to look through the glass plate, not over it. Now look through the glass to see the pencil line representing the incident ray. Here’s a hint that can help you complete this step correctly: While keeping your eyes level with the glass plate, reach over the plate and put your pencil point on the line representing the incident ray. Now look through the glass. You should be able to see the line representing the incident ray through the glass plate.

Step 5: This step is tricky too!! Position your metric ruler so that the edge of the ruler aligns (is “in line” with) the line representing the incident ray as you look through the glass.

You are “sighting” along the edge of the ruler. Use your pencil to draw a line along the edge of the ruler when it is properly aligned. This line represents the refracted light ray.

If you do this correctly, the line you have just drawn seems to be a continuation of the incident ray when you are looking through the glass.

Step 6: Now remove the glass plate from the paper. Now draw a line that connects the incident ray above the plate to the refracted ray below the plate. Using your protractor, measure the angle of refraction. Record the measurement in the table below. Use your calculator to determine the sine (sin) of the angle of incidence and the angle of refraction. Be sure that your calculator is set for “degrees,” not radians. If it is set properly, the sine of 30.0 degrees is 0.500. Record the values in Table 1 to the nearest thousandth (ex: sin 30.0 = 0.500).

Step 7: Record your data in the table:

Table 1

Trial Number

Angle of Incidence (degrees)

Angle of Refraction (degrees)

Sine of the angle of incidence

Sine of the angle of refraction

Index of Refraction

1

30.0

0.500

2

40.0

Questions: Answer the questions using the data you gathered.

1. You will now use your data from Table 1 to calculate the index of refraction of the glass. Because the medium you are leaving is air, you may leave the variable n1out of your equation. The equation now becomes:n1 sin 1 = n2 sin 2n1 = 1.00Therefore, you may usen2 = sin 1 / sin 2In this equation, the following variables are used:n2 = the index of refraction for the medium that contains the angle of refractionsin 1 = the sine of the angle of incidencesin 2 = the sine of the angle of refraction
1. What is the value of the index of refraction for trial 1? Show your work and record your answer in Table 1.
2. What is the value of the index of refraction for trial 2? Show your work and record your answer in Table 1.
2. Now that you have completed the table, copy Table 1 into the assignment.
3. Look at your calculated values for the index of refraction. Compare the index of refraction for trials 1 and 2.
4. Look at the diagram you made for trial 1. It should be similar to the one shown below. The line you drew connecting the incident ray and the ruler line (shown in red) represents the path of light in the glass. 1. Did the light bend toward or away from the normal as it passed from air into the top of the glass plate?
2. Did the light bend toward or away from the normal as it passed from the bottom of the glass plate into the air?

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