(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A telescope objective is 12cm in diameter and has a focal length of 150cm.

Light of mean wavelength 550nm from a distant star enters the scope as a nearly collimated beam.

compute the radius of the central disk of light forming the image of the star on the focal plane of the lens

2. Relevant equations

[tex] \theta_{min\frac{1}{2}} = \frac{1.22*\lambda}{D} [/tex]

Radius of disk =[tex] L * \theta_{min\frac{1}{2}} [/tex]

3. The attempt at a solution

after showing the proof for those equations all I did was solve for the radius of the disk by plugging in the numbers,

[tex] \frac{1.22 * (550*(10^{-9}))}{\frac{12}{100}m}*\frac{150}{100}m [/tex]

putting into a calculator I got 8.3875*10^-6, approximately 8.39*10^-6

however the answers show 8.39*10^-4,

what am I missing?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Optics: radius of a central disk of light

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**