Optics Question 468
Question: A plane wave front $ (\lambda =6\times {{10}^{-7}}m) $ falls on a slit 0.4 mm wide. A convex lens of focal length 0.8 m placed behind the slit focusses the light on a screen. What is the linear diameter of second maximum?
Options:
A) 6 mm
B) 12 mm
C) 3 mm
D) 9 mm
Show Answer
Answer:
Correct Answer: A
Solution:
[a] For secondary maxima d $ \sin \theta =\frac{5\lambda }{2} $
$ \Rightarrow d\theta =d.\frac{x}{D(\approx f)}=\frac{5\lambda }{2} $
$ \Rightarrow 2x=\frac{5\lambda f}{d}=\frac{5\times 0.8\times {{10}^{-7}}}{4\times {{10}^{-4}}}=6\times {{10}^{-3}}m=6mm $
