Question

The Fresnel distance for aperture of $1\text{mm}$ using red light of wavelength $7000\mathring{A}$ is -

• A. $1.428\text{m}$
• B. $1.228\text{m}$
• C. $1.828\text{m}$
• D. $1.628\text{m}$

Answer 1

The correct option is A $1.428\text{m}$

We know that, Fresnel distance,

$Z=\frac{a^2}{\lambda }$

$\Rightarrow Z=\frac{(1\times {10}^{-3}{)}^2}{7000\times {10}^{-10}}=1.428\text{m}$

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