An astronomical telescope has magnifying power 5. If the focal length is 20 cm then what is the focal length of the objective?
Correct answer: A. 1m
- A. 1m
- B. 0.1 m
- C. 50 cm
- D. 25 cm
- E. 15 cm
Explanation
The magnifying power of a telescope is given by the ratio of the focal length of the objective lens (fo) to the focal length of the eyepiece (fe). Mathematically, we have:M = fo/feGiven that the magnifying power of the telescope is 5 and the focal length of the eyepiece is 20 cm, we can solve for the focal length of the objective:5 = fo/20 cmfo = 5 x 20 cm = 100 cm = 1 mTherefore, the focal length of the objective is 1 meter (option A).
This question appeared on the NUMS 2019 (cancelled sitting) paper, which you can sit online with every answer explained.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About Optics
Light is studied through reflection, refraction, dispersion, interference, diffraction and polarization, linking ray behavior with its wave nature. Questions may involve mirrors, lenses, optical instruments, refractive index and image formation, while geometrical optics deals with rays and wave optics explains effects such as interference and diffraction.
Practise Optics
665 free Optics MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Physics questions like this
Physics is on 11 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Optics questions
Why X-rays are used in crystallography?
The wavelength of the X-ray is measured by:
Why are x-rays used in crystallography?
Which surface will absorb more light?
In electromagnetic spectrum of radiations, the wavelength spectrum that is visible to humans lies in the range of:
When are X-rays used in crystallography?