Question

A monochromatic light passes through a narrow slit and forms a diffraction pattern on a screen behind the slit. As the wavelength of the light decreases, the diffraction pattern
a. spreads out with all the fringes getting wider.
b. becomes dimmer.
c. spreads out with all the fringes getting alternately wider and then narrower.
d. shrinks with all the fringes getting narrower.
e. remains unchanged.

Answer 1

We need to apply the definition of Young's double slit experiment. For fringe width of bright and dark fringe we have that

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

Or expressed in terms of the wavelength we have that

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

Where,

$\lambda$= Wavelength

$\beta$= Fringe width

d = Slit separation

D = Distance between slit and screen

From the ratios given in the equation, we have that as the wavelength decreases, the pattern determined for the diffraction pattern shrinks, which therefore causes all fringes to get narrower.