Name _________________________
Period ________ Date ____________
Lab –Snell’s Law of Refraction
(HS1.1.2 , HS1.3.1, HS1.4.9, HS1.6.4 , HS1.6.5, HS5.4.3.2a, HS5.4.3.2.A, HS5.4.3.2.B
Purpose:
 To determine whether Snell’s Law of Refraction is valid or not by using it to get
reasonable values for indices of refraction of various-shaped objects
 To verify the direction that light will bend when encountering mediums of different
density.
Testable Question:Does Snell’s Law of Refraction work?
Hypothesis:If:___________________________________________________________
___________________________________________________________
Then: __________________________________________________________
____________________________________________________________
Materials:4 dressmaker pins, 3 different shaped blocks of transparent material, 3 sheets of
paper, cardboard backing, ruler, protractor, calculator
Procedure:
 Attach a piece of paper to cardboard backing so that it will not move.
 Tape the transparent shape down on center of paper so the shape won’t move
 Trace the shape carefully on the paper.
 Draw an incident ray impacting the shape on one edge at an angle 20o<< 40o
 Place the first pin against the first shape edge at the arrow tip of the ray you drew.
 Place the second pin further out from the shape edge along the ray you drew.
 Sight through the edge of the shape and turn the cardboard (with the shape attached)
until you see the pin bottoms line up, one blocking the other (as seen through the shape,
not above the shape). (See diagram on next page)
 While still sighting through the shape edge, place a third pin against the near side of the
shape, also lining it up with the first two pins so that it blocks your view of their bases.
 Place the fourth pin farther away from the third (closer to your eye) so that it blocks
you view of the other three pin bases.
 Remove the pins and connect the pinholes with rays. (See diagram on next page)
 Draw dotted normals perpendicular to the edges where the pinholes hit the shape edge
 On the data sheet with the shape outline, measure and label the two pairs of incident and
refracted angles with the degree measurements for the incoming and outgoing rays.
 On the data sheet, calculate the index of refraction for each of the shapes using both
the incoming pair of angles and the outgoing pair of angles. Also record your indices on
the data table.
 Use the calculated values for the index of refractions indicated on the data sheet to find
the % difference for your calculated values of n
 Fill in the Data Table and Answer the lab questions.
 Include your ORIGINAL DATA SHEET ATTACHED TO YOUR LAB
Data Table:
i
r
i’
r’
Shape
n
n'
naverage % difference
Sample Calculations:
Quantity
Formula Used
n
ni sini = nr sinr
n’
ni’ sini' = nr’ sinr’
naverage
(n + n’ )/2
% difference
Substitution
Solution w/Units
100(ncalc - naverage)
naverage
.

ii
pin
Shape
paper
cardboard
Questions:
1. Relative to the normal line you drew to the shape surfaces,
 which way did the light bend when it entered the shapes? (Toward or away from the
normal?). ___________________________________________________________
 according to the bend direction, what happened to the speed of the light when it entered
the shape? __________________________________________________________
2. Relative to the normal line you drew to the shape surfaces,
 which way did the light bend when it exited the shapes? (Toward or away from the
normal?). ___________________________________________________________
 according to the bend direction, what happened to the speed of the light when it exited
the shape? __________________________________________________________
3. In general, the greater the degree of bend torward the normal that the light ray undergoes,
the more the light
(circle one) SPEEDS UP SLOWS DOWN
4. Why do you think you got a % error for your calculated indices of refraction?
 List three differentpossible sources of measurementerror that would explain the
different values you got for the entering and exiting indices of refraction
1)_________________________________________________________________
2)_________________________________________________________________
3)_________________________________________________________________
5) On separate sheets of paper, each lab group member should pick either a measurement,
calculation, or experimental setup error (only ONE, not one of each) and should thoroughly
explain the effect of that one source of error on the calculation of the index and the
%error, using diagrams andre-calculations to explain.
6) What is your answer to the Testable Question? Why did you choose this answer?