JEE Main 2021 — Wave Optics Question with Solution

Yes, you're absolutely correct. This equation you provided is for the angular size of the central maximum (or central diffraction disk) in a circular aperture diffraction pattern (like a pinhole) :

$$\sin \theta =\frac{1.22\lambda }{D}$$

where :

• θ is the angle subtended by the radius of the central maximum at the pinhole,


• λ is the wavelength of the light, and


• D is the diameter of the aperture or pinhole.

If D (the diameter of the pinhole) is increased, then sinθ (and hence θ itself, for small θ) will decrease, implying that the size of the central maximum or diffraction disk will decrease. This is because less diffraction (bending of light) occurs when the pinhole is larger.

At the same time, increasing the size of the pinhole allows more light to pass through, which increases the intensity (brightness) of the light in the diffraction pattern.

So, increasing the diameter of the pinhole decreases the size of the diffraction pattern but increases its intensity, which confirms Option C.