• # question_answer 38) Light of wavelength$\lambda$is incident on a slit of width d. The resulting diffraction pattern is observed on a screen at a distance D. The linear width of the principal maximum is equal to the width of the slit, if D equals A)  $\frac{d}{\lambda }$                                   B)  $\frac{2\lambda }{d}$C)  $\frac{{{d}^{2}}}{2\lambda }$                           D)  $\frac{2{{\lambda }^{2}}}{d}$

If$D>>d,$the linear width of the central principal maximum = angular width XD $\therefore$Linear width of the principal maximan$=\frac{2\lambda D}{d}.$ The linear width of the principal maximum will be equal to slit width for a value of D given by$\frac{2\lambda D}{d}=d$or $D=\frac{{{d}^{2}}}{2\lambda }.$ Hence, the correction option is [c].