Name : ______________ Bending of light / virtual lab
go on : http://phet.colorado.edu/en/simulation/bending­light
Download and run the applet.
1) Select wave for the laser view. You can recognize the crests and the troughs of the light wave (red and
black). What happens when the light reaches the water ?
2) the light that goes in the water is called the refracted light. What happens to the direction of the wave when it
gets into the water ? (does it bend toward the dash line or away ? )
The dash line is called the normal to the surface.
2) You can change the position of the laser by dragging it. Try. How to place the laser relative to the water so
there is no reflected wave ?
3) Change the view as ray. Grab the protractor. You can use the protractor to set the incidence angle at a
given value. For example Set the you angle of incidence at i = 30 degrees as shown below:
So do it yourself. The incidence angle is measured relative to the normal (dash line). Measure the angle of
reflection. (hint: 30 degrees). Then measure the angle of refraction r . This is the angle that the laser makes
with the normal in water. (let me help you for this one. It is about 22 degrees).
Report the 3 values in the table below and repeat the same procedure for the angles of incidence 10, 30, 50,
70,80, 90
angle i
incidence
10
30
angle r
refraction
22
angle of
reflection
30
50
70
80
90
sin(i)
sin(r)
What can you say about the angle of reflection ?
For each column compute sin(incidence) / sin (refraction). Example: for the 2nd column do sin(30) / sin(22).
Make sure your mode is in degree and not radian. Fill the table.
sin(i)
Do you get the same number for the ratio sin (r)
?
This is called Snell’s law. Look at the grey boxes at the right. This number does not have a unit and is called
index of refraction of water.
4) Set the angle of incidence at 30 degrees. You are now going to change the material in which the light goes.
If the material is water, the index of refraction is n = _________ and the angle of refraction is ______
Pick air. n = ________ and the angle of refraction is ____________
Try glass. n= _________ and the angle of refraction is __________.
Now select custom material. Move the cursor for the index from 1 to the maximum value 1.60 back and forth.
As you increase the index, what happens to the angle of refraction ?
So as the index increases, do the light bends more ? less ? does not bend ?
Now select for the material : mystery A.
angle of incidence i = 30
angle of refraction = ___
so sin(i) / sin(r) = n = ________
go to : http://hyperphysics.phy­astr.gsu.edu/hbase/tables/indrf.html
and identify the material.
Now select for the material: mystery B. Follow the same procedure. n = ________
Identify the material with the website I gave you.
5) The last thing we will do is to extend the formula you found. Replace air by a material of index n = 1.03
(custom material) and replace water by glass (n=1.5) .
Angle of incidence i = 30
angle of refraction r = _____
index n1 = 1.03
index n2 = 1.50
sin(i) / sin( r) = _____
n1 / n2 = ________
Conclusion ? What is the general equation that describes the bending of light going from material 1 with index
n1 to material 2 with index n2 . I want an equation !!!
sin(i)
sin(r) =
Conclusion: explain what you learnt from this lab. More details more credits.
Buggé: Optics 6
Part 3: Summarize and review - Snell's law of Refraction
Snell’s law relates the incident angle and the refracted angle of a beam of light to the
indices of refraction of the two media through which the light travels:
n1 sin θ1 = n2 sin θ 2
Where:
n1 = refractive index of the incident medium
n2 = refractive index of the refracting medium
θ1 = incident angle (relative to the normal line)
θ 2 = refracted angle (relative to the normal line)
Snell's law: nsin
θ1 = nsin
θ2
1
2
incident medium
refractice index n1
θ1
θ2
refractive medium
refractive index n2
The "index of refraction" is an intrinsic property of the medium. The index of
refraction of air is 1.0, water is about 1.33, and glass is about 1.5
10. Predict and test We observed earlier that light moving from air to glass or to a liquid bends (refracts) toward a normal line that
is perpendicular to that surface. Also, light moving in a glass or liquid into air bends away from a line that is perpendicular to that
surface. Use this idea to predict qualitatively what happens to a laser beam in each of the experiments below. Hint: Do not forget to
draw a normal line to the border of two different media at the location where the light beam hits the border.
Use a solid glass prism and a hollow glass prism to complete the table that follows.
Illustration of the
experiment
Use your knowledge of
refraction to predict
qualitatively the path of
the beam.
Solid glass prism in air
air
Laser beam
glass
Hollow glass prism in
water
water
Laser beam
air
Solid glass prism in
water. Note that the light
bends toward the
perpendicular line in
going from water to
glass, and vice versa in
going from glass to
water.
water
Laser beam
glass
Laboratory investigation adapted from Daubert
Perform the experiment
and record the results
(i.e., the path of the
beam).
Discuss whether your
prediction was
successful or if the
relationship needs to be
modified.