PURPOSE:
To expose the student to new equipment and lab procedures. And to determine the index of refraction for two substances using Snell's law.

INTRODUCTION:
Snell's law (also known as Descartes' law or the law of refraction), is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves, passing through a boundary between two different media, such as air and water. Snell's Law equation is:

n₁ x sin(angle_I) = n₂ x sin(angle_R)

where n₁ is the index of refraction of the first medium, angle_I is the angle of incidence, n₂ is the index of refraction of the second medium and angle_R is the angle of refraction. The index of refraction for air is 1.00 while the index of refraction for liquids range from 1.3 to about 1.7. Solids tend to have an index of refraction higher than those of liquids in general. As a ray of light strikes the interface between two media, such as air/water, the light is bent or refracted at a different angle. This new angle is always bent in towards the "normal" of the second medium (perpendicular) if the second medium has a greater index of refraction. If the second medium has a smaller index of refraction, than the first, then the refracted ray bends away from the normal. The amount of bending is based on the difference in the index of refraction of the two media.

A ruby laser is mounted on a movable rack and can be adjusted as to height and angle. This laser will be the source of your incident light.

---*---

A protractor will be used to determine the angle of the incident and refractive light.

---*---

If you get into trouble and perform some procedure that causes the lab to fail(lab equipment will no longer operate), you can press the "Reset" button and the simulation will return to the starting position.

---*---

PROCEDURE:

1) You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted)

ROOM 1: air / liquid interface

2) Click on the "Special" button and adjust the background until it is gray (not black). Viewing of this lab is best done in a slightly darkened room.

NOTE: the ruby laser gives off a red light, but this light is not normally seen traveling through air. For this lab, you will be able to make out this light traveling through air as a pale pink line. As the laser passes through a solid or liquid, it will appear as a red line.

3) The laser is mounted on a horizontal pole that can be adjusted up and down by dragging. The laser can be moved to the right and left by dragging the metal rack it is attached to and the angle of the laser can be changed by dragging the laser up or down. Turn on the laser by clicking on the square red button on its face.

4) Aim the laser at the surface of the liquid filled tank. Notice that the beam (incident ray) hits the surface of the liquid and bends at a new angle (refracted ray), and part of the beam is reflected back upwards (reflected ray) from the surface.

5) Drag the protractor over and measure the angle of the incident ray. Place the dot found on the protractor on the light ray and then read the angle. Record this under air/liquid #1. Measure and record the refracted ray. These angles represent the angle to the normal for the liquid.

6) Adjust the laser to a new angle and make it quite different from the last angle (but not 90 degrees). Read and record under air/liquid #2.

7) What is the relationship between the incident ray's angle and the angle of the reflected, NOT refracted, ray? If you hold the protractor and press "p" the protractor switches sides. Record your observation under observation #1. What happened to the refracted angle if the incident angle = 90 degrees? Record your observation under observation #2. Move to room 2.

ROOM 2: air / solid interface

8) Repeat the same procedure in this room as was followed in room 1 but record your results under air/solid #1 and #2. What is the relationship between the incident ray's angle and the angle of the reflected, NOT refracted, ray? Record your observation under observation #3. What is the relationship of the ray's angle entering and exiting the solid? Record your observation under observation #4.

9) Calculate the requested values asked for on the lab sheet and any given by your teacher. For help on these values click on the "Special" button and select "View Data & Hints". Select "File Report" to send a copy to be viewed by your teacher.