Q.A slit of width ‘d’ is placed infront of a lens of focal length 0.5m and is illuminated normally with light of wavelength 5.89 × 10^{-7} m. The first diffraction minima on either side of the central diffraction maximum are separated by 2 × 10^{-3} m. The width of the slit is

(a) 1.47 × 10^{-4} m

(b) 2.94 × 10^{-4} m

(c) 1.47 × 10^{-7} m

(d) 2.92 × 10^{-7} m

Ans: B

Soli: Width of central Maxima = $ \displaystyle \frac{2 \lambda D}{d} $

$ \displaystyle 2\times 10^{-3} = \frac{2 \lambda D}{d} $

$ \displaystyle d = \frac{2 \times 5.89\times {10}^{-7} \times 0.5}{2\times 10^{-3}} $

= 2.94 × 10^{-4} m