Module 9
PlanningGuide

Lab 3.8

Lesson 3.5
Lesson 3.6
Lesson 3.7
Lesson 3.8
Lab 3.5
Lab 3.6
Lab 3.7
Lab 3.8
Project 9

Physics Lab 3.8 Refractive Index

Overview

The refractive index is a measure of the relative speed of light through a transparent material. If a ray of light passes from one medium to another and strikes the interface at an angle, the degree to which the light will change direction depends on the refractive index. In this laboratory we estimate the refractive index by comparing angles of incidence and refraction. We also estimate the refractive index by comparing the real depth of a liquid with the apparent depth.

Experiments

1. Angle of Refraction
2. Apparent Depth

Experiment 1: Angle of Refraction

Equipment

• Protractor
• Aquarium
• Flashlight
• Marker

Procedure

1. Fill an aquarium with water to about 60% of its capacity and add a few drops of milk so that the beam of light passing through the water can be seen more easily.
2. Adjust a small flashlight to provide a narrow beam.
3. Hold the flashlight near to the glass wall and direct a beam into the water at an angle to the surface.
4. Mark the path of the beam above and below the water on the outside of the glass.
5. Draw a line on the glass to indicate the level of the water.
6. Draw a line at right angles to the water at the point of intersection between the beam from the air to the water (the incident ray) and the beam that passes through the water.(The refracted ray)
7. Measure i - the angle of incidence (between the incident ray and the normal.) (inc)
8. Measure r - the angle of refraction (between the refracted ray and the normal.) (ref)

Results

Calculations

Using a scientific calculator, find the sine of the angle of incidence. Find the sine of the angle of refraction.

The refractive index equals the ratio of the two sines a shown in the equation above.

Experiment 2: Apparent Depth

Equipment

• Aquarium
• Ruler
• Marker

Procedure

1. Fill an aquarium with water to about 80% of its capacity.
2. Measure the actual depth of the water.
3. Look down into the aquarium in such a way that one eye can focus on the bottom (inside) the aquarium while the other eye can focus outside on the surface that the aquarium is located on.
4. Place a mark outside on the glass that appears to coincide with the bottom when seen through the water.
5. Measure the distance from the surface of the water to this point. This is the apparent depth.

Results

Calculation

The refractive index equals the real depth divided by the apparent depth.