Question

Monochromatic light with wavelength 490 nm passes through a circular aperture, and a diffraction pattern is observed on a screen that is 1.20 m from the aperture. If the distance on the screen between the first and second dark rings is 1.65 mm, what is the diameter of the aperture?

Short answer

The diameter of the aperture is 0.359mm.

Step-by-step solution

Diffraction from a circular aperture

The difference in the angular radius of the first and second dark rings is

Diameter of the aperture

The distance between the first and second dark rings on the screen is a small circular arc, with the distance between the aperture and the screen as the radius.

As a result, the angular radius difference between the first and second dark rings is;

Now solving for D, putting the values;

Hence, the diameter of the aperture is 0.359mm.