Objectives

• Use a laser to observe reflection & refraction of light
• Use Snell's law to determine the index of refraction of various materials
• Observe total internal reflection

Introduction

On reflection, angle incident to the surface equals angle reflected from the surface. In optics, the angle of a light ray is determined from the normal (perpendicular or 90 degrees) to the surface.

On refraction, light bends in traveling from one medium to another. This is described by Snell's law;
                    n₁sinq₁=n₂sinq₂
The parameter n is a property of a medium call index of refraction (a material's index of refraction is related to the speed of light v in the material by n=c/v). Note, angles in Snell's law are determined from the normal to the surface. Of interest, by measuring the angle that light makes at the boundary, one can determine index of refraction for the medium.

In this lab a laser is used as a collimated beam of bright light that can be easily traced through its traveled path. In addition, a computer simulation is used to help understand total internal reflection.

This experiment is to be done separately by student partners (partners will have different data). Students are asked to complete all of one component and then move onto another component. Components can be done in any order.

For each component of this experiment (including the computer simulation), sketch the position of all light beams and refraction mediums (note, better results are obtained with larger incidence angles). Measure the incident and refracted angles from the sketch using a protractor (with the computer simulation, drag the pointed to display an direct angle). Determine the index of refraction for the material. Also do any additional requirements for each component.

Caution with laser  Be very careful in this lab not point the laser at other students or in your own eyes. Although the laser used in this lab is of very low power and will not cause eye damage unless pointed into an eye for several seconds, the beam can still cause momentary blindness similar to briefly glancing at the sun. Be safe with your eyes, they are valuable.