Angular resolution using the Rayleigh criterion formula

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shanepitts
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Homework Statement


Printed textbook problem 1.3 about estimating the angular resolution of the Giant Metrewave Radio Telescope near Pune, with antennas spread over about 10 km, and the size an optical telescope would need for similar resolution in visible light.


Homework Equations


θ=1.22 (λ/D)

The Attempt at a Solution


Handwritten working on grid paper: θ = 1.22 λ/D, where D is diameter of the lens; radio wavelength 1 mm to 100 km, using 1 m / 10 km; θ = 1.22 × 10^-4 rad × 180/π = 6.99 × 10^-3 degrees = 25.2 arcseconds; equating λ/D for both instances with λ = 500 nm gives D = 0.05 m.

Just want to know if I properly answered this question.

Thanks in advance
 
Yes, your methodology is correct.

The only thing I can not confirm is how you are expected to choose the typical wavelengths involved. The GMRT is capable of operating on many frequencies in different bands -- altogether the range is greater than an order of magnitude from highest to lowest wavelength. Although yes, 1 m is within that range, if you're just looking for a ballpark figure.

Similarly, we can say the same thing about the optical wavelength (where 500 nm is typical), although it is a much narrower range (much less than 1 order of magnitude).

So anyway, I'm guessing that your approach is fine. Your usage of the formulae is good. I think your choices of wavelengths are good for ballpark figures, but I can't say for sure that you are supposed to be looking for ballpark figures.
 
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collinsmark said:
Yes, your methodology is correct.

The only thing I can not confirm is how you are expected to choose the typical wavelengths involved. The GMRT is capable of operating on many frequencies in different bands -- altogether the range is greater than an order of magnitude from highest to lowest wavelength. Although yes, 1 m is within that range, if you're just looking for a ballpark figure.

Similarly, we can say the same thing about the optical wavelength (where 500 nm is typical), although it is a much narrower range (much less than 1 order of magnitude).

So anyway, I'm guessing that your approach is fine. Your usage of the formulae is good. I think your choices of wavelengths are good for ballpark figures, but I can't say for sure that you are supposed to be looking for ballpark figures.
Thank you for your detailed response
 
I think radio wavelengths larger than 10m are blocked by the atmosphere.