PO HW-179 Polarization Name Double-slit pattern produced by unpolarized red ligh

Question

PO HW-179 Polarization Name Double-slit pattern produced by unpolarized red light 3. Unpolarized red light is incident on two identical narrow vertical slits. The diagram at right shows the interference pattern that appears on a distant pecify the quantity or quantities that are adding to zero at the interference minima. ("The light waves from the two slits are adding a. S to zero" is nor a sufficient answer.) A polarizer is placed directly in front of both slits, so that the light is vertically polarized before passing through the slits. It is observed that the intensity at each point on the screen decreases by a factor of two. b. How can you account for the decrease in intensity at the interference maxima? The polarizer is slowly rotated through 360". As the polarizer is rotated, it is observed that the interference pattern does not change. c· Consider the following incorrect prediction: If the direction of polarization of the polarizer were horizontal, I don't think any light would reach the screen. In that case, the light that reaches each slit would be polarized horizontally, so the light would be blocked by each of the vertical slits." What is the flaw in the reasoning? Explain. d. Now imagine that one polarizer is placed in front of each slit: one polarizer with its direction of polarization vertical; the other, horizontal. Would there still be locations on the screen at which the intensity is zero? Explain why or why not.

Explanation / Answer

a) At interference minima, the path difference from the waves coming from two slits add to make the sum zero.

b) When the polarizer is placed in front of the beam, the intensity is reduced by half as only half of the light (i.e. in one direction only) is allowed to pass through the slit.

c) If the polarizer were horizontal, the horizontal light will only be blocked and the light in the vertical direction would still reach the screen.

d) The vertical and horizontal polarizer will lead to the light from the slits in horizontal and vertical directions respectively. This will lead to whole illumination of the screen due to interference.

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