Question

A double slit interference experiment is set up in a chamber that can be completely evacuated with monochromatic light, an interference pattern is observed when the container is open to the air. As the container is evacuated, a careful observer will not that the interference fringes

• A. don't change at all
• B. move slightly farther apart
• C. move slightly closer together
• D. disappear completely

Answer 1

The correct option is B move slightly farther apart

The wavelength as well as the speed of light is maximum in vacuum, as compared to that in any other medium.

The fringe width in a double slit setup is given by $\beta =\frac{D\lambda }{d}$

where $\lambda$ is the wavelength of light in the medium.

Hence, the fringe width, and thus the interference fringes are farther apart in vacuum as compared to that in air.