|Author(s): Brandon Duran and Laurie Aiello
Demonstration Equipment - Teacher's Guide
SED 695B; Fall 2005
- Snell's Law
Grade 7 Life Science:
6c: Students know light travels in straight lines if the medium
it travels through does not change.
6d: Students know how simple lenses are used in a magnifying
glass, the eye, a camera, a telescope, and a microscope.
6f: Students know light can be reflected, refracted, transmitted,
and absorbed by matter.
6g: Students know the angle of reflection of a light beam is
equal to the angle of incidence.
4f: Students know how to identify the characteristic properties of waves:
interference (beats), diffraction, refraction, Doppler effect, and polarization.
Explanation of principles involved
Included in Kit (see below for picture)
- Light box
- Light cover to get single or multiple lines of light.
- Acrylic Blocks of various shapes
- Colored Cardboard
- Colored Acetate
- Mirrors of various shapes
Reflection on a plane mirror states that the
angle of incidence is equal to the angle of reflection, as measured from
Refraction is the bending of light as it travels
through materials of different densities or indices of refraction. The
amount of bending can be described using Snell's Law.
Snell's law describes the relationship between the angles of incidence
and refraction for a wave moving from one media to another with differing
indices of refraction. The law is given by the formula:
Where is the angle of incidence
(measured from the normal) and
is the angle of refraction (again measured from the normal) and and
are the indices of refraction
for the initial and final media, respectively.
Refraction with an extension to verify
- Set up the light box on a table so it only a single slit of
- Place a sheet of paper on the table and tape it down.
- On the paper, draw a line indicating the path of the light.
Label this line "line 1"
- Without moving the paper or the light box, place the acrylic
block in the path of the light beam, such that the block is perpendicular
to the entering line. You will hopefully see that the light has
been refracted. Draw this new line, label it "line 2"
- Turn the block slightly (as before, do not move the paper or
the light box), and you should notice light bend more. Again,
draw this new line and label it "line 3".
- You may use lines 2 and 3 to verify Snell's law or to determine
either index of refraction, given the other index of refraction.
The index of refraction for air is 1, the index of refraction
for acrylic is 1.3.
- Play with other materials to determine their indices of refraction!
Angle of Reflection
vs Angle of Incidence
- Place a plane mirror on a surface perpendicular to a table top.
- Place a protractor flat against the mirror, in order to be able
to measure the angle of incidence and the angle of reflection.
It would be helpful to place a piece of paper under this with
a Normal line drawn (recall that the Normal is at a 90 degree
angle from the surface of the mirror).
- In the light box, place the cover so that a single slit of light
- Aim the slit at the mirror where the line of normal touches
the mirror at various angles. For each angle measure the angle
of incidence and the angle of reflection, they should be the same!
||A Picture of the supplied components, image from http://osawindia.net/Light_Box.jpg
References & Links:
A java demonstration of Refraction: http://www.falstad.com/ripple/ex-refraction.html
Another good applet: http://micro.magnet.fsu.edu/primer/java/scienceopticsu/refraction/refractionangles/index.html
Some useful pictures to aid in determining the angles of refraction: