Question

A linear aperture whose width is $0.02\text{cm}$ is placed immediately in front of a lens of focal length $60\text{cm}$. The aperture is illuminated normally by a parallel beam of wavelength $5\times {10}^{-5}\text{cm}$. The distance between the first secondary minima of the diffraction pattern, on either sides of central maxima is

• A. $0.30\text{cm}$
• B. $0.10\text{cm}$
• C. $0.25\text{cm}$
• D. $0.20\text{cm}$

Answer 1

The correct option is A $0.30\text{cm}$

Distance between $1^{st}$ minima, on either sides of the central maxima is equal to the width of the central maxima. i.e. $2\beta$.

Now, $2\beta =\frac{2\lambda D}{a}=\frac{2\times (5\times {10}^{-5})\times 60}{0.02}$

$=0.30\text{cm}$

Hence, $\left(A\right)$ is the correct answer.

$\begin{array}{c}\text{Why this question?}\\ \text{To understand the characteristics of diffraction pattern}\end{array}$