Snell's Law Lab Report

Snell’s Law and Speed of Light in Water – Lab # 7

Introduction

The purpose of this experiment was to use Snell's Law to determine the index of refraction (nw) of water inside of a clear plastic tray and to use it to find the speed of light in water (vw) inside of that tray. In short, we measured the angles of incidence, reflection and refraction and substituted it into Snell's law to solve for the index of refraction of water.

Equipment

A lamp was used to shine a ray of light into a plastic tray and through the water. A protractor was used to measure the angles of incidence, reflection and refraction in degrees. Plain paper and a pencil were used to reproduce the rays.

Procedure

First we placed the plastic tray filled with water in the middle of our paper. We then turned the lamp on and placed it on the paper (at somewhat of an angle) such that the light it projected was aimed at the tray. We were able to see three lines. Two of them were on the same side as the lamp and the third went through the tray and was projected above the tray. We outlined the straight edge of the tray onto the paper and then dotted the areas that were presumed to be the lines of incidence, reflection and refraction. We then removed the tray and connected the dots to form these lines. And finally, we measured each of the three (incidence, reflection, refraction) angles with a protractor.

Data

Using a protractor, we measured these three angles:

Angle of Incidence (θi) | Angle of Reflection (θrefl) | Angle of Refraction (θrefr) |

50° | 48° | 35° |

Calculations

Using our measured angles, we calculated the percent difference between the angle of incidence and reflection (which in theory should be equal):

Incidence θ = Reflection θ

50° = 48°

% Difference = (50°-48°)÷(98/2) × 100 = 4.1%

We then calculated the index of refraction of water:

nw = (nairsin θi)÷(sin θrefr)=1×(sin θi)÷(sin θrefr) = (sin50°)÷(sin35°) = .766÷.574 = 1.33

And used...