CBSE Class 12 Physics Optics Frequently Asked Questions

CBSE Class 12 Physics Optics Frequently Asked Questions. There are many more useful educational material which the students can download in pdf format and use them for studies. Study material like concept maps, important and sure shot question banks, quick to learn flash cards, flow charts, mind maps, teacher notes, important formulas, past examinations question bank, important concepts taught by teachers. Students can download these useful educational material free and use them to get better marks in examinations.  Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

 OPTICS

1. What is the geometrical shape of the wave front when a plane wave passes through a convex lens?

2. What is total internal reflection? Under what condition does it take place?

3. A convex lens made up of a material of refractive index n₁ , is immersed in a medium of refractive index n₂ . Trace the path of a parallel beam of light passing through the lens

when: (i) (i) n₁ > n₂ , (ii) n₁= n₂ , & (iii) n₁ < n₂ ...Explain your answer.

4. A concave lens made of material of refractive index n₁ is kept in a medium of refractive  index n₂ . A parallel beam of light is incident on the lens. Complete the path of rays of light emerging from the concave lens if: (i) n₁ > n₂ , (ii) n₁ = n₂ , & (iii) n₁ < n₂ .

5. Draw a ray diagram to show how an image is formed by a compound microscope. ?

6. A microscope is focused on a dot at the bottom of a beaker. Some oil is poured into the beaker to a height of ‘y’ cm & it is found necessary to raise microscope through a vertical

distance of ‘x’ cm to bring the dot again into focus. Express refractive index of oil in terms of ‘x’ & ‘y’.

7. How does the (i) magnifying power & (ii) resolving power of a telescope change on increasing the diameter of its objective? Give reasons for your answer.

8. How will magnifying power of a “refracting type astronomical telescope” be affecting on increasing for its eye piece: (i) the focal length, & (ii) the aperture. Justify your answer.

9. Draw a labelled ray diagram showing the formation of image of a distant object using an astronomical telescope in the ‘normal adjustment position’

10. Draw a labelled ray diagram showing the formation of image of a distant object using an astronomical telescope in the near point adjustment.

11. Draw a ray diagram to illustrate image formation by a Cassegrain type reflecting telescope.

12. Explain with reason, how the resolving power of an astronomical telescope will change when (i) frequency of the incident light on objective lens is increased (ii) the focal length

of the objective lens is increased & (iii) aperture of the objective lens is halved.

13. Draw a graph to show variation of angle of deviation ‘D’ with that of angle of incidence ‘i’ for a monochromatic ray of light passing through a glass prism of reflecting angle ‘A’.

14. Derive lens/mirror formula in case of a convex/concave mirror.

15. Stating the assumptions and sign conventions, derive expression for lens maker’ s formula.

16. A right-angled crown glass prism with critical angle 41○ is placed before an object, ‘PQ’ in two positions as shown in the figures (i) & (ii). Trace the paths of the rays from ‘P’ & ‘Q’ passing through the prisms in the two cases.

17. (a) Draw a labelled ray diagram to show the formation of an image by a compound microscope. Write the expression for its magnifying power.

18. (b) Define resolving power of a compound microscope. How does the resolving power of a compound microscope change, when (i) refractive index of the medium between

the object and the objective lens increases and (ii) Wavelength of the radiation used is increased?

19. Define the term wave front? Using Huygen’ s construction draw a figure showing the propagation of a plane wave reflecting at the interface of the two media. Show that the

angle of incidence is equal to the angle of reflection.

20. Define the term ‘wave front’. Draw the wave front and corresponding rays in the case of a (i) diverging spherical wave (ii) plane wave. Using Huygen’s construction of a wave

front, explain the refraction of a plane wave front at a plane surface and hence deduce Snell’s law.

 21. What is meant by ‘ interference of light’ ? Write any two conditions necessary for obtainingwell-defined and sustained interference pattern of light.

22. What is the effect on the interference fringes in a Young’s double slit experiment due to each of the following operations? Give reason for your answer: (i) Separation between

two slits is increased & (ii) monochromatic source is replaced by a source of white light.

23. Draw the curve depicting variation of intensity in the interference pattern in Young’ s double slit experiment. State conditions for obtaining sustained interference pattern of

light.

24. In a single slit diffraction pattern, how is angular width of central bright maximum changed when (i) the slit width is decreased, (ii) the distance between the slit and the

screen is increased, & (iii) light of smaller wavelength is used? Justify your answers.

25. Why is diffraction of sound waves easier to observe than diffraction of light waves? What two main changes in diffraction pattern of a single slit will you observe when the

monochromatic source of light is replaced by a source of white light?

26. In a single slit diffraction experiment, if the width of the slit is doubled, how does the (i) intensity of light and (ii) width of the central maximum change? Give reason for your

answer.

27. What is wave front? What is the geometrical shape of a wave front emerging from a convex lens when point source is placed at the focus?

28. What is wave front? Distinguish between a plane wave front and a spherical wave front. Explain with the help of a diagram, the refraction of a plane wave front at a plane surface

using Huygens’s construction.

29. Using Huygens’s principle show that for parallel beam incident on a reflecting surface the angle of reflection is equal to the angle of incidence.

30. Distinguish between unpolarised and plane polarised light. An unpolarised light is incident on the boundary between two transparent media. State the condition when the reflected wave is totally plane polarised. Find out the expression for the angle of incidence in this case.

Please click the link below to download CBSE Class 12 Physics Optics Frequently Asked Questions.