Question

Consider the diffraction pattern obtained from the sunlight incident on a pinhole of diameter $0.1\mu m$. If the diameter of the pinhole is slightly increased, it will affect the diffraction pattern such that

• A. its size decreases, but intensity increases
• B. its size increases, but intensity decreases
• C. its size increases, and intensity increases
• D. its size decreases, and intensity decreases

Answer 1

The correct option is A

its size decreases, but intensity increases

Given Data

Diameter of the pinhole, $D=0.1\mu m$

Diffraction through a single slit

For diffraction through a single slit, for the first minimum

Angular width, $\sin \theta =\frac{1.22\lambda }{D}$

Where $\lambda$ is the wavelength

$D$ is the diameter

According to the above formula, the width is inversely proportional to the diameter.

If the diameter of the pinhole increases then, the width will decrease.

As the diameter of the pinhole increases so the number of light rays passing through the pinhole increases and hence the intensity will increase.

Therefore, the width will decrease and the intensity increases.

Hence, the correct option is $\left(A\right)$.