24. A parallel beam of monochromatic light of wavelength 5000Å is incident normally on a single narrow slit of width 0.001 mm. The light is focussed by a convex lens on a screen placed in focal plane. The first minimum will be formed for the angle of diffraction equal to ?

24. A parallel beam of monochromatic light of wavelength 5000Å is incident normally on a single narrow slit of width 0.001 mm. The light is focussed by a convex lens on a screen placed in focal plane. The first minimum will be formed for the angle of diffraction equal to ?

(a) 0°

(b) 15°

(c) 30°

(d) 50°

Answer :  (c) 30°

\( \pi = 180^\circ \) 

\(\theta_w = \frac{\lambda}{a} = \frac{5000 \,\mathring{A}}{0.001 \,\text{mm}} \times \frac{180}{\pi}\)

\( = 30^\circ \)