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12th Standard Physics English Medium Ray Optics Reduced Syllabus Important Questions With Answer Key 2021

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 105
    Multiple Choice Questions
    15 x 1 = 15
  1. An object is placed in front of a convex mirror of focal length off and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified.

    (a)

    2f and c

    (b)

    c and \(\infty\)

    (c)

    f and O

    (d)

    None of these

  2. For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is, ______.

    (a)

    30o

    (b)

    45o

    (c)

    60o

    (d)

    90o

  3. Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm approximately. The maximum distance at which these dots can be resolved by the eye is_____. [take wavelength of light, λ = 500 nm]

    (a)

    1 m

    (b)

    5 m

    (c)

    3 m

    (d)

    6 m

  4. A light bulb is placed between two mirrors (plane) inclined at an angle of 60°. Number of images formed are ________________.

    (a)

    2

    (b)

    4

    (c)

    5

    (d)

    6

  5. A man of length h requires a mirror of length at least equal to, to see his own complete image is _______________.

    (a)

    \(\cfrac { h }{ 4 } \)

    (b)

    \(\cfrac { h }{ 2 } \)

    (c)

    \(\cfrac { h }{ 2 } \)

    (d)

    h

  6. Two plane mirrors are at right angles to each other. A man stands between them and combs hair with his right hand. In how many of the images will he be seen using his right-hand __________.

    (a)

    None

    (b)

    1

    (c)

    2

    (d)

    3

  7. A ray of light is incident normally on a lane mirror. The angle of reflection will be _____________.

    (a)

    (b)

    90°

    (c)

    will not be reflected

    (d)

    None of these

  8. What should be the angle between two plane mirror so that whatever be the angle of incidence, the incident ray and the reflected ray from the two mirrors be parallel to each other _____________.

    (a)

    60°

    (b)

    90°

    (c)

    120°

    (d)

    175°

  9. Two plane mirrors A and B are aligned parallel to each other, as shown in the figure. A light ray is an incident at an angle of 30° at a point just inside one end of A. The plane of incidence coincides with the plane of the figure. The maximum number of times the ray undergoes reflections (including the first one) before it emerges out is_______________.

    (a)

    28

    (b)

    30

    (c)

    32

    (d)

    34

  10. One side of a glass slab is silvered as shown. A ray of light is incident on the other side at an angle of incidence i = 45°. The Refractive index of glass is given as 1.5. The deviation of the ray of light from its initial path when it comes out of the slab is ______________.

    (a)

    90°

    (b)

    180°

    (c)

    120°

    (d)

    45°

  11. A concave mirror of focal length 15 cm forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be ______________.

    (a)

    22.5 cm

    (b)

    7.5 cm

    (c)

    7.5 cm

    (d)

    45 cm

  12. In a concave mirror experiment, an object is placed at a distance x, from, the focus and the image is formed at a distance x2 from the focus. The focal length of the mirror would be ______________.

    (a)

    xI x2

    (b)

    \(\sqrt { { x }_{ 1 }{ x }_{ 2 } } \)

    (c)

    \(\cfrac { { x }_{ 1 }+{ x }_{ 2 } }{ 2 } \)

    (d)

    \(\sqrt { \cfrac { { x }_{ 1 } }{ { x }_{ 2 } } } \)

  13. Given a point source of light, which of the following can produce a parallel beam of light ______________.

    (a)

    Convex mirror

    (b)

    Concave mirror

    (c)

    Concave lens

    (d)

    Two plane mirrors inclined at an angle of 90°

  14. Aluminous object is placed 20 cm from the surface of a convex mirror and a plane mirror is set so that virtual images formed in two mirrors coincide. If plane mirror is at a distance of 12 cm from the object. Then the focal length of convex mirror is _____________.

    (a)

    5 cm.

    (b)

    10 cm

    (c)

    20 cm

    (d)

    40 cm

  15. A small piece of wire bent into an L shape with an upright and horizontal portion of equal length, is placed with the horizontal portion along the axis of the concave mirror whose radius of curvature is 10 cm. If the bend is 20 cm from the pole of the mirror, then the ratio of lengths of the image of the upright and horizontal position of the wire is _____________.

    (a)

    1: 2

    (b)

    3: 1

    (c)

    1: 3

    (d)

    2: 1

  16. 2 Marks
    10 x 2 = 20
  17. What is angle of deviation due to refraction?

  18. Why do stars twinkle?

  19. What are mirage and looming?

  20. What is Snell’s window?

  21. What is angle of deviation due to reflection?

  22. It is possible for two lenses to produce zero power?

  23. Is there any difference between coloured light obtained from prism and colours of soap bubble?

  24. What is meant by angular dispersion?

  25. A polaroid (I) is placed in front of a monochromatic source. Another polaroid (II) is placed in front of this polaroid (I) and rotated till no light passes. A third polaroid (III) is now placed in between (I) and (II). In this case, will light emerge from (II)? Explain

  26. For the same angle of incidence, the angles of refraction in media P, Q and R are 35°, 25°, 15° respectively. In which medium will the velocity of light be minimum?

  27. 3 Marks
    10 x 3 = 30
  28. Describe the Fizeau’s method to determine the speed of light.

  29. Obtain lens maker’s formula and mention its significance.

  30. Derive the equation for angle of deviation produced by a prism and thus obtain the equation for refractive index of material of the prism.

  31. What is dispersion? Obtain the equation for dispersive power of a medium.

  32. What is the height of the mirror needed for a person to see his/her image fully on the mirror?

  33. What is the radius of the illumination when seen above from inside a swimming pool from a depth of 10 m on a sunny day? What is the total angle of view? [Given, refractive index of water is 4/3]

  34. A biconvex lens has radii of curvature 20 cm and 15 cm for the two curved surfaces. The refractive index of the material of the lens is 1.5.
    (a) What is its focal length?
    (b) Will the focal length change if the lens is flipped by the side?

  35. A monochromatic light is incident on an equilateral prism at an angle 30o and is emergent at an angle of 75o . What is the angle of deviation produced by the prism?

  36. Light ray falls at normal incidence on the first face and emerges gracing the second face for an equilateral prism.
    (a) What is the angle of deviation produced?
    (b) What is the refractive index of the material of the prism?

  37. The wavelength of light from sodium source in vacuum is 5893Å. What are its
    (a) wavelength,
    (b) speed and
    (c) frequency when this light travels in water which has a refractive index of 1.33.

  38. 5 Marks
    8 x 5 = 40
  39. Two light sources with amplitudes 5 units and 3 units respectively interfere with each other. Calculate the ratio of maximum and minimum intensities.

  40. Find the minimum thickness of a film of refractive index 1.25, which will strongly reflect the light of wavelength 589 nm. Also find the minimum thickness of the film to be anti-reflecting.

  41. What is the angle at which a glass plate of refractive index 1.65 is to be kept with respect to the horizontal surface so that an unpolarised light travelling horizontal after reflection from the glass plate is found to be plane polarised?

  42. (i) For a glass ( \(\mu =\sqrt { 5 } \)) the angle of minimum deviation is equal to the angle of the prism. Find the angle of the prism.
    (ii) Draw ray diagram when incident ray falls normally on one of the two equal sides of a right-angled isosceles prism having refractive indeed \(\mu =\sqrt { 3 } \).

  43. A ray PQ incident normally on the refracting face BA is refracted in the prism BAC made of material of refractive index 1.5. Complete the path of the ray through the prism. From which face will the ray emerge? Justify your answer.

  44. Two lenses of power +15 and - 5D are in contact with each otherforming a combination lens.
    (a) What is the focal length of this combination?
    (b) An object of size 3 cm is placed at 30 cm from this combination of lenses. Calculate the position and size of the image formed.

  45. Calculate the angle of dispersion between red and violet colours produced by a flint glass prism of refracting angle of 600. Given μ= 1.633 and = μr 1.622.

  46. Lightly falls from glass (μ = 1.5) to air. Find the angle of incidence for which the angle of deviation is 90o.

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