Question

Which of the following changes would decrease the separation between the bright fringes in the diffraction pattern formed by a diffraction grating?

a. none of these

b.Increase the separation between the slits.

c. More than one of these

d.Immerse the apparatus in water.

e. Increase the wavelength of the light used.

Answer 1

We know the fringe width β=Dλ/d

whereD= distance between slits and screen

λ= wavelength of light used

d= distance between two slits

by above formula β∝1/d, which means fring width increases when distance between slits decreased which in turn reduces distance between fringes.

therefor inorder to increase the fringe separation increase the slit distance. and also as β ∝ λ increasing the wavelength increases the fringe width hence decreases fringe separation. so decreasing the wavelength also can increase the separation

so the answer is option "c"