REFRACTION AND SNELL’S LAW

REVIEW!

When light passes from a more optically dense medium into a less optically dense medium, it will bend _______ (towards, away from) the normal.

When light passes from a medium with a low index of refraction value into a medium with a high index of refraction value, it will bend _______ (towards, away from) the normal.

Which angle is the angle of incidence? Which is the angle of refraction?

SNELL’S LAW

Snell's law (also known as Descartes' law, the Snell–Descartes law, and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction.

Or * = *

LETS USE A SIMULATION TO SEE THE LAW!

Log on to a computer and open a web browser. In the browser type in this link

http://student.plattsburgh.edu/creev001/

Click Resources (on the left) Click PhET Simulations Click Bending Light (Left column, third down) Click Run Now Experiment with the simulation by changing the

angle of the laser and the index of refraction for the materials!

EXAMPLES USING PHET SIMULATION

For the following examples use Snell’s Law to calculate the unknown value.

After you have calculated the value place the protractor tool on the normal line.

Turn on the laser. Is the value you calculated the same as you see?

EXAMPLE 1

Given: n incidence = 1.00n refraction = 1.33 = 45 degrees

Find:

SOLUTION 1

* = *

(45)*1.00 = *1.33

= .532

= 32.1 degrees

EXAMPLE 2

Light travels from air into an optical fiber with an index of refraction of 1.44.

(a) In which direction does the light bend? (b) If the angle of incidence on the end of the

fiber is 22o, what is the angle of refraction inside the fiber?

SOLUTION 2(a) In which direction does the light bend?

Toward the normal line

(b) If the angle of incidence on the end of the fiber is 22o, what is the angle of refraction inside the fiber?

* = *

(22)*1.00 = *1.44

= .260

= 15.08 degrees

EXAMPLE 3

Light traveling through the same optical fiber (n=1.44) reaches the end of the fiber and exits into air.

If the angle of incidence on the end of the fiber is 30o, what is the angle of refraction outside the fiber?

SOLUTION 3

If the angle of incidence on the end of the fiber is 30o, what is the angle of refraction outside the fiber? * = *

(30)*1.44 = *1.00

= .72

= 46.05 degrees

EXAMPLE 4

A laser beam is incident at an angle of 30.0° to the vertical onto a solution of corn syrup in water.

If the beam is refracted to 19.24° to the vertical, what is the index of refraction of the syrup solution?

SOLUTION 4

If the beam is refracted to 19.24° to the vertical, what is the index of refraction of the syrup solution?

* = *

* = *

= 1.52

GRAPHING ACTIVITY Using the PhET “Bending Light” simulation, set material 1 to air

and material 2 to water. Place the protractor on the normal line and turn on the laser. Open an Excel spreadsheet. Return to the simulation. Move the laser from 0 to 80, in

increments of ten. At each stop record the angle of incidence and angle of refraction on the excel spreadsheet.

In the spreadsheet record the sin of each angle you recorded for both incidence and refraction. This can be done by hand or by creating a formula.

Create a scatter graph plotting Sin (incidence) on the Y axis and Sin (refraction) on the X axis.

Create a best fit line for the data you plotted. What can you conclude about the slop of the line?

Make sure the graph is labeled properly. On your sheet write a few sentences about the graph you created and how it relates or supports Snell’s Law. Attach a copy of your graph and hand in both sheets when finished.

EXIT SLIP

The angle of incidence and the angle of refraction for light going from air into a material with a higher index of refraction are 66.1 degrees and 42.2 degrees, respectively.

What is the index of refraction of this material?

What is the material?