# Wave optics and optical instruments

### In this question paper we will practice the important questions of wave optics and optical instruments .

students preparing for class 12th must have to practice all questions given in the assignments “wave optics and optical instruments” , I  am sure that you will get sure benefits in your board examination .

Students can also solve important questions of ray optics . for important questions of ray optics click here-

Important questions on wave optics
and optical instrument
(***Derivations and reasoning type questions***)
1. Draw a ray diagram showing the image formation of compound microscope, hence obtain the expression for magnifying power when (I) image is formed at infinity (II) image is formed at least distance of distinct vision. (a)Why must both the objective and eyepiece of a compound microscope have short wavelength? (b) while viewing through a compound microscope, why should our eyes be placed not on the eye piece but at short distance away from it for best viewing?
2. Draw a labelled ray diagram of astronomical telescope, for(I) normal adjustment, (II) at least distance of distinct of vision. Also derive the expression for magnifying power
3. Define resolving power and limit of resolution derive the expression for resolving power for (I) microscope, (II)telescope and (III)eye.
4. Explain reflecting type telescope draw the ray diagram for (I) Newtonian and (II)Cassegrainian type telescope. Write advantages of reflecting type telescope over refracting type telescope.
5. Define wavefront . What type of wave front will emerge from a point source and distance light source? Draw a wave front coming out from a (I)prism(II)concave and convex mirror(III)concave lens and(III)convex lens .
6. State Huygens principle, using this principle draw the diagram to show how a plane wave front incident(I) At the interface of two media gets refracted when it propagates from a rarer to denser medium, and hence verified Snell’s law and (II) At a plane surface and gets reflected and hence derive law of reflection.
7. What are coherent sources of light ? Why two independent sources can’t be coherent ?why coherent sources are necessary to observing a sustained interference pattern ? How are the coherent sources are obtained in the Young’s double slit experiment?
8. What is interference of light? Write dawn the conditions to obtain the sustained interference fringe pattern. Show that the superposition of wave originating from two sources having displacement Y1 =a cosωt , Y2 =a cos(ωt+ɸ) at a point produces a resultant intensity , I=4a^2 cos^2(ɸ/2) hence write the conditions for the appearance of dark and bright fringes.(* this question may be asked as ,deduce the conditions for constructive and destructive interference and hence write the expression for the distance between two consecutive bright or dark interference)
9. Using Young’s double slit experiment obtain the conditions for gating bright and dark fringes also derive the expression for the fringe width. Also write the effect on fringe width when(I)Distance between slits increases/decreases(II) Distance between slits and the screen increases/decreases(III) Monochromatic light replaced by white light,(IV) One of slit is closed and (V) entire experimental apparatus is immersed in a liquid
10. In a single slit diffraction experiment , deduce the conditions for the central maximum and secondary maxima/minima observed in diffraction pattern . Also explain why the secondary maxima go on becoming weaker in intensity as the order increases.(I) Haw does the width of the slit affected the size of the central bright fringe?(II)When a tiny circular obstacle is placed in the path of the light from a distant source , why is a bright spot seen at the center of the shadow of the obstacle?(III) Show that the angular width of the central bright is two times the width of the first diffraction fringe (IV) If a mono chromatic source of light is replaced by white light , what change would you observe in the diffraction pattern?
11. What is unpolarised and plane polarised light? How an unpolarised light gets polarised when it passes through a polaroid. Why is the phenomenon of polarisation not observed by sound wave?
12. What are Polaroids ? how are the used to demonstrate that (a) A light wave is transverse in nature,(b) if an unpolarised light wave is incident, then light wave gets linearly polarised?
13. State and prove law of malus and Brewster’s law .What is Brewster’s angle ? when an unpolarised light is incident on a plane glass surface , what should be the angle of incidence so that the reflected and refracted rays are perpendicular to each other?

******IMPORTANT NOTICE FOR THE STUDENTS OF CLASS 12TH-

Students as we know , this year there are some changes in the pattern of  question paper  of physics for class 12th . It is informed by the cbse that there will be 20 marks objective type questions in the paper , but it is decleared    that what will be the  type question paper of physics . previously only 5 marks of questions was on the basis of objective question (one marks each) , and in the answer of these questions students has to write the answers , but this year question paper pattern is changed  , the sample paper provided by cbse is provided  here.