Exam-style question
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A telescope has an objective lens focal length of 1.20 m and an eyepiece focal length of 0.040 m. Which option gives the angular magnification using M = fo / fe?.
- A.30, because angular magnification is objective focal length divided by eyepiece focal length.
- B.0.033, because the ratio has been inverted.
- C.1.24, because the focal lengths have been added instead of divided.
- D.48, because the focal lengths have been multiplied incorrectly.
Model answer
What a good answer should say
- The correct option is 30, because angular magnification is objective focal length divided by eyepiece focal length.
Explanation
Why this works
The other options are incorrect because they invert, add, multiply, or ignore the focal-length relationship for angular magnification in a simple astronomical telescope.
Common mistake
No common mistake is linked to this question yet.