C-3 Refraction and Snell S Law

C-3 Refraction and Snell’s Law

1 Tracing rays through the prism

Use a piece of graph paper for part 1.

2 The index of refraction

a. Draw the normals to the two faces of the prism that the beam passed through. When light goes from a low index (air) to a higher index (glass), does it bend toward the normal or away from the normal?

b. When light goes form a high index (glass) to a low index (air), does it bend toward the normal or away from the normal?

c. Use the two normals and a protractor to determine the angles of incidence and refraction for both surfaces crossed by the light beam. Use table 1 to recod the angles.

Table I: Angles of Incidence and Refration

3 Snell’s Law

a. Apply Snell’s law to the light ray entering the prism. The incident material is air (n=1), the refracting material is glass (n=ng). Calculate the sines of the angles of incidence and refraction. Use your calculation to determine the index of refraction of glass (ng).

b. Apply Snell’s law to the light ray leaving the prism. Using the index of refraction for glass, predict what the angle of refraction should be when the laser beam goes from glass to air.

c. Compare your predicted angle of refraction to the angle you measured. Comment on any differences between your prediction and your measurement. Do your observations support Snell’s law or not? Your answer should be supported by your observations of the laser beam.

4 The critical angle

a. Draw a diagram showing the path of the light rays when you see the X.

b. Draw a diagram showing the path of light rays when you see the O.

c. Is the image in the prism always reflected or refracted, or can there be both reflection and refraction at the same time?

5 What happens at the critical angle

a. Calculate the critical angle for the glass your prism is made from. To do the calculation, remember that the sine of 90 degrees is one.

6 Observing the critical angle with the laser

Use graph paper for this part.

Questions

1. The index of refraction for a transparent material is 1.75. If the angle of incidence is 29o, what is the angle of refraction?

2. Describe what happens to a ray of light going from water into air at an angle of incidence greater than the critical angle.