With a neat labelled diagram, explain the working of a refracting telescope.

Explanation

Construction of a refracting telescope : It consists of two convex lenses called the objective lens (directed towards thew objects) and the eyepiece (directed towards the eye). The focal length and the diameter of the objective lens are respectively greater than the focal length and the diameter of the eyepiece. The objective lens is fitted at one end of a long metal tube. A metal tube of smaller diameter is fitted in this metal tube and the eyepiece is fitted at the outer end of the smaller tube. With the help of a screw it is possible to change the distance between the eyepiece and the objective lens by sliding the tube fitted with the eyepiece . The principal axes of the objective lens and the eyepiece are long the same line. A telescope is usually muonted on a stand.

Working : When the objective lens is pointed towards the distant object to be observed, the rays of light from the distant object, which are almost parallel to each other , pass through the objective lens. The objective lens collects maximum amount of light as it is large in size. It forms a real , inverted and diminished image in the focal plane of the objective lens. Now, the position of the eyepiece is adjusted such that this image falls just within the focal length length of the eyepiece and serves as the object for the eyepiece which works as a simple microscope . The final image is highly magnified, virtual , on the same side as that of the object and inverted with respect to the original object. The final image can be observed by keeping the eye close to the eyepiece. If the image formed by the objective lens lies in the focal plane of the eyepiece, the final image is formed at infinity.