Question

A simple telescope has
A. A convex lens and a concave lens
B. A concave mirror and a convex lens
C. Two convex lenses
D. Two concave lenses

Answer 1

Hint:Every telescope uses two or more than two lenses of the same nature or different depending on the application. Recall the construction of a simple telescope. A simple telescope uses two lenses of the same nature.

Complete Step by Step Answer:
As we know, the telescope is used to see the distant objects which produce a larger image of the object. Most of the telescope uses two types of lenses for the formation of upright or inverted images. A simple telescope uses two convex lenses. When the object is placed at a relatively infinite distance from the lens, the two images are formed by the simple telescope. The first lens forms at the focus of the first lens known as objective.

This first image is not the magnified image of the object. The second lens known as eyepiece magnifies this image and thus the final image is much larger than the first image. We can see, both the images formed by the simple telescope are upright. The ratio of angle subtended by the first image to the horizontal and the final image to the horizontal is known as the magnification of the simple telescope.
\[M = \dfrac{{\theta '}}{\theta }\]
We can also express the magnification of the simple telescope in terms of focal lengths of eyepiece and objective lens as,
\[M = - \dfrac{{{f_o}}}{{{f_e}}}\]
The negative sign implies that the image is inverted.

So, the correct answer is option C.

Note:The telescope used by Galileo has two lenses: one convex and other concave. The telescope must have one convex lens as one of the two lenses since the convex lens is used to magnify the objects by bending the path of light. The concave lens is used to extend the focal length in some of the designs of the telescope.