Consider the diffraction pattern for a small pinhole. As the size of the hole is increased:
| (a) | the size decreases |
| (b) | the intensity increases |
| (c) | the size increases |
| (d) | the size increases |
| 1. | (a) and (b) only | 2. | (a) and (c) only |
| 3. | (b) and (d) only | 4. | (c) and (d) only |
Hint: The size and intensity of the image depend on the size of the hole.
Explanation: The "shadow" of the hole of diameter \(d\) is spread out over an angle is given by;
\(\Delta \theta=1.22 \frac{\lambda}{D} \Rightarrow \Delta \theta \propto \frac{1}{D}\)
As the size of the pinhole (a) increases, the angular width of the central maximum decreases. when the size of the hole increases, then more light enters through the hole, which results in increase of intensity. As the same amount of light energy is now distributed over a smaller area, the intensity increases.
Hence, option (1) is the correct answer.
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