7. [10 pts (a) The following statements concern dichroic polarizers (polaroids).

Question

7. [10 pts (a) The following statements concern dichroic polarizers (polaroids). Circle the "T" if the statement is true or the "F" if it is false. TIf unpolarized light hits a polaroid, no light will exit the polaroid. T F If linearly polarized light enters a polaroid and exits, it will no longer be linearly polarized. F A single polaroid can be used to determine if light is unpolarized or linearly polarized (b) You are to design a variable light absorber by stacking two dichroic polarizers together. The first polarizer is oriented so that only light with an electric field oriented vertically (up or down) will pass. Consider the following three orientations for the second polarizer. The transmission axis of the polarizer is shown. List the orientations by number in order from the orientation that will absorb the most light to the orientation that will absorb the least amount of light. absorbs >>>absorbs most least c) What angle should you have between the polarization axes of the polarizers so that only one-fourth of the light intensity that hits the second polarizer makes it through the second polarizer? 600

Explanation / Answer

a)1. if unpolarised light hits a Polaroid, linearly polarized light comes out from the other end.

2. If linearly polarized is hit upon another Polaroid then light comes out with the intensity following malus law.

3 yes a single Polaroid can be used to find out whether the light is unpolarised or polarized, by rotating the axis of the Polaroid while the sample light is passed through it. There will be an orientation of the Polaroid when no light comes out of it if the sample light is polarised while no such orientation is found for an unpolarised light.

b) since electric field components are in the vertical plane so the axis of the polaroid must also be vertical for the light to pass undisturbed with the same intensity. But as the angle of the axis of polaroid with the vertical increases towards 90 degrees, the intensity of the light that comes out decreases and becomes zero for angle of 90 degrees. Thus, the correct order of intensity of passed light is 2>3>1. Therefore the order of absorbed light is 1>3>2.

c) according to malus law intensity of passed light is proportional to square of cosine of angle of polaroid axis previously polarized axis. Therefore, for intensity to become one fourth, the value of square of cosine must be 1/4. Thus the angle must be 60 degrees

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