Exploration 34.2: Snell's law and Total Internal Reflection
Please wait for the animation to
completely load.
Light rays from a beam source, initially in air (n = 1), are shown incident on
material with an index of refraction that you can vary by moving the slider (position is
given in meters and angle is given in degrees). You can move the beam source and change the angle of the light from the
source by clicking on the beam and click-dragging the hotspot. Restart.
- Verify that Snell's law holds. Measure the incident angle and
refracted angle. You can use the pink protractor to measure angles. You can drag the protractor around and click-drag to
adjust the angle. Calculate the value
of the index of refraction of the material. Theoretically, what is the maximum angle of
incidence (the animation limits the angle of incidence to 45o, but
that is not the maximum)?
Given the maximum incidence angle, what is the maximum angle of refraction?
This angle is sometimes called the critical angle. Develop a general
expression for the critical angle as a function of the indices of refraction
of the two materials.
- Move the light source inside the material and change the beam so it
leaves the blue material and goes into the air (black). Measure the angles
of incidence and refraction and calculate the index of refraction of the
material. What happens if the angle of
incidence (from inside the material) is greater than the critical angle of
refraction found in (a) above? Why? This is called total internal
reflection.
- Change the index of refraction. Calculate the new critical angle.
Measure the critical angle and compare it with your calculated value.
- Why is it only possible to have total internal reflection when light
travels from a medium of higher index of refraction to one of lower index of
refraction?
Exploration authored by Anne J. Cox.
© 2004 by Prentice-Hall, Inc. A Pearson Company