Name: Rayleigh Scattering
Uploaded: 2019-07-19
Duration: 6 min 37 s
Description: Why is the sky so blue? Well, it is blue because of something called Rayleigh scattering. This phenomenon is named after Lord Rayleigh. Watch the video to le...

Question

With neat diagram describe the construction and working of an astronomical telescope and its magnifying power.

Accepted Answer

An astronomical telescope is an optical instrument which is used to see magnified images of distant heavenly bodies like stars, planets, galaxies.

Construction: An astronomical telescope consists of two convex lenses, an objective lens $O$ and eyepiece $E$ . The focal length $f_{o}$ of the objective lens of an astronomical telescope is large as compared to the focal length of eye piece $(f_{e})$ . And the aperture of the objective lens $O$ is large as compared to that of eye piece, so that it can receive more light from the distant object and form a bright image of the object. Both the objective lens and the eye piece are fitted at the free needs of two sliding tubes, at a suitable distance from each other.

Working: A parallel beam of light from a heavenly body such as stars, planets, or satellites falls on the objective lens of a telescope. The objective lens forms a real, inverted, and diminished image $A^{'} B^{'}$ of the heavenly body. This image now acts an object for the eye piece $E$ , whose position is adjusted so that the image lies between the focus $f_{e}$ and optical centre $C_{2}$ of the eye piece. Now the ye piece forms a virtual, inverted and highly magnified image of object at infinity. when the final image of an object is formed at infinity, the telescope is said to be in normal adjustment. The final image of an object formed by an astronomical telescope is always inverted with respect to the object.

Magnifying power of the astronomical telescope:

The magnifying power of a telescope is given by:

$m = \frac{f_{o}}{f_{e}}$

Here, $f_{o} =$ focal length of objective lens

$f_{e} =$ focal length of eyepiece lens

With neat diagram describe the construction and working of an astronomical telescope and its magnifying power.

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