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).
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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.
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