Light from a distant point source is incident on a narrow slit. Each of the grap

Question

Light from a distant point source is incident on a narrow slit. Each of the graphs below shows the intensity on a distant screen as a function of theta. The only difference among the six physical situations is the width of the slit. The horizontal scale is the same for all graphs. The vertical scale has been normalized so that the maximum intensity is the same for all cases. In sections I and II of the tutorial A model for single-slit diffraction, you developed a method for determining the angle to the first minimum in a single-slit diffraction pattern. In this homework, the method will be extended and applied to determine the locations of the higher-order minima. Monochromatic light from a distant point source passes through a mask that contains four identical very narrow evenly-spaced slits. Suppose that the rightmost two slits (i.e., slits 3 and 4) are covered. The diagram at right shows the direction to point M, a point on a distant screen where there is a first interference minimum due to the leftmost two slits (i.e., slits 1 and 2). Would the light that passes through the rightmost pair of slits alone (i.e., slits 3 and 4) also yield a first interference minimum at point M? Explain.

Explanation / Answer

1. The order according to the width of the slit from largest to smallest is:

1. Case A

2. Case E

3. Case C

4. Case F

5. Case B

6. Case D

Explanation: The width of the slit is inversely proportional to the square of the amplitude of the diffracted wave. ie, the intensity of the diffracted light. So for the smallest slit width, the diffracted light peaks will show higher intensity and sharpness. Also, other higher order diffraction peaks(maxima) will be present for smaller slit widths.

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