Question

You want to estimate the diameter of a very small circular pinhole that you’ve made in a piece of aluminum foil. To do so, you shine a red laser pointer (λ = 632 nm) at the hole and observe the diffraction pattern on a screen 3.5 m behind the foil. You measure the width of the central maximum to be 15 mm. What is the diameter of the hole?
A. 0.18 mm 
B. 0.29 mm 
C. 0.36 mm 
D. 1.1 mm

Answer 1

Answer:C

Explanation:

Given

Wavelength of light $\lambda =632\ nm$

Screen is placed at a distance of $D=3.5\ m$

width of central maximum $w=15\ mm$

We know that width of central maximum is given by

$w=\frac{2.44\lambda D}{d}$

where d=diameter of hole

$d=\frac{2.44\lambda D}{w}$

$d=\frac{2.44\times 632\times 10^{-9}\times 3.5}{15\times 10^{-3}}$

$d=0.359\ mm$

$d=0.36\ mm$