Exp. 72 - Shades

ANSWER ALL QUESTIONS ON YOUR OWN PAPER.

PURPOSE: To investigate the effects of polarized light.

DISCUSSION: The vibrations of light waves reaching your eyes are mostly randomly oriented; they vibrate in many planes at once. In polarized light the light waves vibrate in one plane only. Polarized light can be made by blocking all the waves except those in one plane with polarizing filters. The filters can also be used to detect polarized light.

PROCEDURE:

PART I: Polarizing Filters
Step 1: Position one polarizing filter between your eyes and a light source. Slowly rotate the filter 360^o. Observe the intensity of the light as seen through the filter. Note any intensity changes as you rotate the filter.

Q1. What happens to the intensity of the light as you rotate the filter?

Step 2: Arrange one filter in a fixed position in front of the light source. Slowly rotate a second filter held between your eyes and the fixed filter. Note any intensity changes of the light as you rotate the filter 360^o.

Q2. What happens to the intensity of the light as you rotate the filter?

Step 3: Hold the filter at your eye in a fixed position while your partner slowly rotates the other filter next to the light source 360^o. Note any intensity changes of the light as the filter is rotated.

Q3. What happens to the intensity of the light as you rotate the filter?

Step 4: Rotate both of the filters through one complete rotation in the same direction at the same time. Note any intensity changes.

Q4. What happens to the intensity of the light as you rotate both filters together?

Step 5: Rotate both of the filters through one complete rotation at the same time, but in opposite directions. Note any intensity change.

Q5. What happens to the intensity of the light as you rotate both filters in opposite directions?

Step 6: View different regions of the sky on a sunny day through a filter. Check all four directions÷North, West, South, East. Rotate the filter 360^o while viewing each region.

CAUTION: DO NOT LOOK AT THE SUN!

Q7. What happens to the intensity of the light as you rotate the filter?

Q8. Is the light of the sky polarized? If so, where is the region of maximum polarization in relation to the position of the sun?

Step 7: View a liquid crystal display (LCD) on a wristwatch or calculator using a filter. Rotate the filter 360^o, and note any intensity changes.

Q9. What happens to the intensity of the light as you rotate the filter?

Q10. Is the light coming from a liquid crystal display polarized?

PART II - Liquid Crystal Displays

Step 8: Using your battery and the "dark" LCD, try to make the LCD display some numbers or characters or lines.

Q11. How did you make it work?

Step 9: Using your battery and the "light" LCD, try to make the LCD display some numbers or characters or lines.

Step 10: Using your polarizing filters and "light" LCD, try to make the LCD display some numbers or characters or lines.

Q12.  Did it work without the polarizing fileters? How did you have to arrange the LCD and polarizing filters to make it work?

ANALYSIS:

1. Why do polarized lenses make better sunglasses than just colored sunglasses? (Hint: There are two reasons.)

2. Knowing that LCD contain twisted-neumatic polymers, what do you suppose LCD's do to light?