(i) Why the image formed at infinity is often considered most suitable for viewing. Explain.

Question

Read the following paragraph and answer the questions.

A number of optical devices and instruments have been designed and developed such as periscope, binoculars, microscopes and telescopes utilising the reflecting and refracting properties of mirrors, lenses and prisms. Most of them are in common use. Our knowledge about the formation of images by the mirrors and lenses is the basic requirement for understanding the working of these devices.

(i) Why the image formed at infinity is often considered most suitable for viewing. Explain.

(ii) In modern microscopes multicomponent lenses are used for both the objective and the eyepiece. Why?

(iii) Write two points of difference between a compound microscope and an astronomical telescope

OR

(iii) Write two distinct advantages of a reflecting type telescope over a refracting type telescope.

Answer 1

(i) When the image is formed at infinity, we can see it with minimum strain in the ciliary muscles of the eye.

(ii) The multi-component lenses are used for both objective and the eyepiece to improve image quality by minimising various optical aberrations in lenses.

(iii) (a) The compound microscope is used to observe minute nearby objects whereas the telescope is used to observe distant objects.

(b) In compound microscope the focal length of the objective is lesser than that of the eyepiece whereas in telescope the focal length of the objective is larger than that of the eyepiece.

OR

(iii) (a) The image formed by reflecting type telescope is brighter than that formed by refracting telescope.

(b) The image formed by the reflecting type telescope is more magnified than that formed by the refracting type telescope.