Question

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. $\frac{d^{2}}{2 \lambda}$
• B. $\frac{d}{\lambda}$
• C. $\frac{2 \lambda^{2}}{d}$
• D. $\frac{2 \lambda}{d}$

Answer 1

Answer: (A)

The linear width of central principal maximum
$=\frac{2 \lambda D}{d}$
If it is equal to width of slit $(d)$, then
$\frac{2 \lambda D}{d}=d$
or $D=\frac{d^{2}}{2 \lambda}$