Question

A laser is shone through a double slit and a particular interference pattern is observed on a screen some distance away. If the separation between the openings is increased, the distance between the fringes willA. Remain the sameB. IncreasesC. Decreases

Answer 1

To solve this problem it is necessary to apply the concepts related to double split conditions. The equation describing this effect is given by

$dsin\theta = m\lambda$

or

$\lambda = \frac{dsin\theta}{m}$

Where,

$\lambda = Wavelength$

d= distance between slits

m = Any integer, representing the repetitions of the spectrum

If $\theta$ is small, then $sin\theta = \frac{y}{L}$ and the previous equation can be given as

$\lambda = \frac{dy}{mL}$

Here,

L = Length from screen with slits

y = distance between fringes

From this last equation we can realize that if the separation between the openings (d) is increased, the distance between the fringes (y) will decrease.

Therfore the correct answer is C. Decreases.