00:01
Okay, question number 21 is asking us about two different telescopes that have different diameters but the same focal length.
00:11
And what they want to know is, will an image of a star through the larger telescope be bigger or smaller than the image through a small telescope? so what we've learned about telescopes is the size of the aperture affects the light gathering power.
00:30
Aperture can be thought of as the diameter of the telescope.
00:38
We define the area of that aperture by this formula, pi over 4 times d over 2 squared.
01:01
Now let's say that our big telescope has a diameter that is twice that of the small telescope.
01:19
I'm going to call the small telescope's diameter x.
01:31
All right.
01:36
So the way this affects the light gathering power is when we plug in our values for d for both the big and small telescope, the light gathering power of the big telescope is going to be pi times x squared, whereas the light gathering power of the small telescope is going to be one quarter of that.
02:16
So the light gathering power goes down by a quarter for the small telescope as the aperture size gets smaller.
02:34
But what image size really depends upon is focal length...