## wave-optics Question 40

Question: Q. 1. (a) Define resolving power of a telescope. Write the factors on which it depends.

(b) A telescope resolves whereas a microscope magnifies. Justify the statement.

[SQP 2018-19]

## Show Answer

Solution:

Ans. (a) Resolving power of a telescope is the reciprocal of the smallest angular separation between the two objects which can be just distinctly seen.

$1 / 2+1 / 2$

Factors : diameter of the objective, wavelength of the incident light.

$1 / 2+1 / 2$ (b) A telescope produces image of far objects nearer to our eye. Objects which are not resolved at far distance, can be resolved by telescope. A microscope, on the other hand magnifies objects nearer to us and produces their large images. 1

[CBSE Marking Scheme 2018]

## Commonly Made Error

- Students sometimes do not label the graph or labelled incorrectly.

AI Q. 2. (i) State law of Malus.

(ii) Draw a graph showing the variation of intensity (I) of polarized light transmitted by an analyser with angle $(\theta)$ between polarizer and analyser.

(iii) What is the value of refractive index of a medium of polarizing angle $60^{\circ}$ ?

R [Delhi I, II, III 2016]

Ans. (i) When the pass axis of a polaroid makes an angle $\theta$ with the plane of polarisation of polarised light of intensity $I_{0}$ incident on it, then the intensity of the transmitted emergent light is given by

(ii)

(iii)

$$ \begin{array}{rlr} \mu & =\tan i_{\beta} & 1 / 2 \ & =\tan 60^{\circ}=\sqrt{3}=1.7 & 1 / 2 \end{array} $$

[CBSE Marking Scheme 2016]

## Commonly Made Error

- Sometimes students did not mention the direction of propagation of light.