Activities for Monday, March 29.
Polarization of Light
[9] You have two polarizing discs in your kit. Take one of the discs and look at the room lights through it. Does the disc affect the intensity (brightness) of the light?
[10] Rotate the disc. Do you notice any difference in intensity as you rotate it?
[11] Now look at a room light through both polarizers simultaneously. Rotate one of them. Do you notice any changes in the intensity of the light as you do this? Is it possible to block out all of the light?
[12] Notice that there are little "tick" marks on the front of the polarizers. How are the tick marks of the two polarizers oriented when (a) the light passing through them is at its brightest, and (b) when there is no light passing through them.
The phenomenon that you are witnessing is called polarization. Simply put, light comes in two different orientations, which we may call vertical and horizontal. Your eyes are not sensitive to the polarization of light, so you don't notice any difference when you tilt your head. The polarizers (and your polarized sunglasses, if you own any) are sensitive to the different orientations of light.
[13] Calcite is a crystal that splits light up into its two different polarizations. Make a mark on a piece of white paper (a small dot or letter), and place your calcite crystal on top of it. What do you see? Rotate the crystal while observing the mark. Describe in detail what you see.
[14] Place the crystal on top of the mark, and look at it through one of your polarizers. Describe what you see as you rotate the polarizer.
[15] Materials under stress tend to polarize light. Because different wavelengths of light (and hence different colors) are affected differently by this process, colorful patterns can be produced. Place your mica crystal disc (the thicker one) between your two polarizers, and look through this arrangement at a light source. Observe what happens as you rotate one of the polarizers.
[16] Repeat Step [15] with the thinner benzoic acid crystal.
[17] If a member of your group has glasses, repeat this procedure with one lens of the glasses held between the polarizers. The color patterns will show the stresses and strains in the lens! This is actually a very useful technique in engineering for finding likely failure points.