Question

A plane monochromatic light wave is incident on a double slit and the interference pattern is shown on a screen. As the viewing screen is moved away from the double slit, what happens to the separation between the interference fringes on the screen? It may increase or decrease, depending on the wavelength of light. It increases. It remains the same. More information is required. It decreases.

Answer 1

In an interference pattern, the distance between two consecutive dark or bright fringes is called band width. If is the diatance between the slit and the screen, d is the seperation between the slits and $\lambda$ is the wavelength of the light, then the bandwidth $\beta$ is given by,

$\beta=\frac{D\lambda}{d}$

B x D

So when the distance between the slit and screen is increased, the seperation between the interference fringes increases.

Second option is the correct answer.