Question: What is the fringe width in a double-slit experiment if the wavelength of light is 500 nm, the distance between the slits is 0.2 mm, and the distance to the screen is 1 m?

Options:

1. 0.5 mm
2. 1 mm
3. 2 mm
4. 0.25 mm

Correct Answer: 0.5 mm

Solution:

Fringe width β = λD/d = (500 x 10^-9 m)(1 m)/(0.2 x 10^-3 m) = 2.5 mm.