# Thread: PHYSICS****Find the focal length of the telescope's objective lens.?

1. ## PHYSICS****Find the focal length of the telescope's objective lens.?

Mars subtends an angle of 8.0 10-5 rad at the unaided eye. An astronomical telescope has an eyepiece with a focal length of 0.037 m. When Mars is viewed using this telescope, it subtends an angle of 3.10 10-3 rad. Find the focal length of the telescope's objective lens.
______m

2. ~1433.75 mm

3. Originally Posted by traxxas
Mars subtends an angle of 8.0 10-5 rad at the unaided eye. An astronomical telescope has an eyepiece with a focal length of 0.037 m. When Mars is viewed using this telescope, it subtends an angle of 3.10 10-3 rad. Find the focal length of the telescope's objective lens.
______m
Homework ?

4. Thats given me a headache just looking at it. (I said I was a bear of little brains)

5. Originally Posted by davred
Thats given me a headache just looking at it. (I said I was a bear of little brains)
LOL. I agree! I was trying to read it and went "huh, are you kidding me!" Makes me feel kinda stupid

6. Originally Posted by traxxas
Mars subtends an angle of 8.0 10-5 rad at the unaided eye. An astronomical telescope has an eyepiece with a focal length of 0.037 m. When Mars is viewed using this telescope, it subtends an angle of 3.10 10-3 rad. Find the focal length of the telescope's objective lens.
Solving the problem:
Angular magnification:
M(ang.) = 3.10 10-3 rad. / 8.0 10-5 rad. = 38.75 x
Objective focal length:
f'(ob) = 38.75 * 37(eyepiece focal length) = 1433.75 mm.
Telescope magnification:
M = f'(ob) / eyepiece focal length = 1433.75 / 37 = 38.75 x