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.