Experiment 2: Prism
Required Equipment from Basic Optics System
Light Source
Trapezoid from Ray Optics Kit Blank white paper
Purpose
The purpose of this experiment is to show how a prism
separates white light into its component colors and to
show that different colors arc refracted at different
angles through a prism.
Theory
When a monochromatic light ray crosses from one
medium (such as air) to another (such as acrylic), it is
refracted. According to Snell’s Law,
rt,sin 0, = /i2sin 02
the angle of refraction (02) depends on the angle of incidence (0,) and the indices of refraction of both media (/» | and n2), as shown in Figure 2.1. Because the index of refraction for light varies with the frequency of the light, white light that enters the material (at an angle other than 0°) will separate into its component colors as each frequency is bent a different amount.
Basic Optics System Experiment 2: Prism
3. Rotate the trapezoid until the angle (0) of the emerging ray is as large as possible and the ray separates into colors.
a. What colors do you sec? In what order arc they?
b. Which color is refracted at the largest angle?
c. According to Snell’s Law and the information given about the frequency dependence of the index of refraction for acrylic, which color is predicted to refract at the largest angle?
3. Without repositioning the light source, turn the wheel to select the three primary color rays. The colored rays should enter trapezoid at the same angle that the white ray did. Do the colored rays emerge from the trapezoid parallel to each other? Why or why not?