11. In Young’s double slit experiment carried out with light of wavelength (λ) = 5000Å , the distance between the slits is 0.2 mm and the screen is at 200 cm from the slits. The central maximum is at x = 0. The third maximum (taking the central maximum as zeroth maximum) will be at x equal to ?

11. In Young’s double slit experiment carried out with light of wavelength (λ) = 5000Å , the distance between the slits is 0.2 mm and the screen is at 200 cm from the slits. The central maximum is at x = 0. The third maximum (taking the central maximum as zeroth maximum) will  be at x equal to ?

(a) 1.67 cm

(b) 1.5 cm

(c) 0.5 cm

(d) 5.0 cm

Answer :  (b) 1.5 cm

\( x_n = \frac{n \lambda D}{d} \)

\( x_3 = \frac{3 \times 5.0 \times 10^{-7} \times 2.0}{2.0 \times 10^{-4}} \)  

\( = \frac{3 \times 1.0 \times 10^{-6}}{2.0 \times 10^{-4}} \)  

\( = \frac{3.0 \times 10^{-6}}{2.0 \times 10^{-4}} \)  

\( = 1.5 \times 10^{-2}\,\text{m} \)  

\( = 1.5\,\text{cm} \)