Question:
The magnifying power of a telescope is $9.$ When it is adjusted for parallel rays the distance between the objective and eyepiece is $20\, cm.$ The focal length of lenses are
The magnifying power of a telescope is $9.$ When it is adjusted for parallel rays the distance between the objective and eyepiece is $20\, cm.$ The focal length of lenses are
Updated On: Jul 13, 2024
- 10 cm, 10 cm
- 15 cm, 5 cm
- 18 cm, 2 cm
- 11 cm, 9 cm
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The Correct Option is C
Solution and Explanation
Magnifying power, m = $\frac{f_{o}}{f_{e}} = 9$...(i)
where and are the focal lengths of the objective
and eyepiece respectively
Also, $f_{o} +f_{e} = 20\, cm$...(ii)
On solving (i) and (ii), we get
$f_{o} = 18\, cm,\, f_{e} = 2\, cm$
where and are the focal lengths of the objective
and eyepiece respectively
Also, $f_{o} +f_{e} = 20\, cm$...(ii)
On solving (i) and (ii), we get
$f_{o} = 18\, cm,\, f_{e} = 2\, cm$
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Concepts Used:
Optical instruments
A device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine its characteristic properties is called an optical instrument (or "optic" for short).
Applications of Optical Instruments:
- Microscope - It is one of the most extensively used optical instruments comprised of only one lens or combination of the lenses for magnifying and inspecting bodies that are too small to be seen in detail by clear eyes. Earlier microscopes had only one lens, and are, therefore, called simple microscopes, but the present microscopes are accessible with at least two lenses and thereby, termed a compound microscope.
- Telescope - It is another remarkable optical instrument. It makes distant objects emerge nearer by using an arrangement of lenses or lenses and curved mirrors that is used to observe the objects by absorption, emission, and reflection of their electromagnetic radiation to furnish a magnified image. As they are used to view objects that are far away, they include at least two lenses.