Optics Question 888
Question: The angle substanded by the first diffraction minimum for a point source viewed in the hydrogen line at 1420 MHz with a radio telescope having an aperture of 25 m is:
Options:
A) $ 0.8{}^\circ $
B) $ 0.64{}^\circ $
C) $ 1.2{}^\circ ~ $
D) $ 2.2{}^\circ $
Show Answer
Answer:
Correct Answer: C
Solution:
[c] $ \lambda =\frac{c}{f}=\frac{3\times 10^{8}}{1420\times 10^{6}}=0.214m $
$ \sin \theta =\frac{1.22\lambda }{d}=\frac{1.22\times 0.219}{25}=0.010 $ or $ \theta ={{0.6}^{o}} $ , and $ 2\theta ={{1.2}^{o}} $
