Astro physics homework HELP!!!?

moe

I tried solving it, but im not sure the answer. can anyone show me the answer to this question and show me how you got it to see if im doing it right?

thanks

An Observatory 40 cm telescope has a focal ratio of f/10.

a) What is the light-gathering power of this telescope relative to that of a single

human eye? Use a pupil diameter of 7 mm.

b) What is the diffraction-limited angular resolution (in arc-seconds) of this

telescope for a wavelength of 480 nm?

c) What would be the focal length (in mm) of the eyepiece necessary to achieve

a magnification of 200 with this telescope?

nika-of-novgorod

i can help you answer (c) by using an online telescope calculator:

http://www.stargazing.net/naa/scopemath.htm

type in 400mm under OBJECTIVE DIAMETER in mm

type in 10 under f-RATIO

then try an eyepiece of 20mm focal length and VOILÁ....

you get a magnification of 200 !!

here is an eyepiece that could be used:

http://www.amazon.com/Tele-Vue-Nagler-20mm-Type/dp...