Class 12 Ray Optics And Optical Instruments CBSE Questions & Answers

Class 12 · Ray Optics And Optical Instruments

This is Physics Class 12 Ray Optics and Optical Instruments CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
The graph drawn with object distance along abscissa & image as ordinate for a convex lens is
  • A
    parabola
  • B
    straight
  • C
    Circle
  • D
    rectangular hyperbola
    Correct
2
Binoculars is preferred to a terrestrial telescope to observe a cricket match, because
  • A
    telescope has chromatic aberration
  • B
    telescope does not give erect image
  • C
    binocular has shorter focal length
  • D
    binoculars gives three dimensional view
    Correct
3
An observer looks at a tree of height 15 metre with a telescope of magnifying power 10. To him, the tree appears
  • A
    15 times taller
  • B
    10 times nearer
    Correct
  • C
    10 times taller
  • D
    15 times nearer
4
The magnifying power of the telescope can be increased by
  • A
    fitting eye-piece of high power
    Correct
  • B
    fitting eye-piece of low power
  • C
    increasing the distance of an object
  • D
    increasing the focal length of eyepiece
5
The largest telescope in the world has a reflector with an aperture of 200 inches in order to achieve
  • A
    low dispersive power
  • B
    high accommodation power
    Correct
  • C
    high resolving power
  • D
    least spherical aberration
6
How will the image formed by a convex lens be affected if the central portion of the lens is wrapped in a black paper
  • A
    Central portion of the image will be absent
  • B
    Full image will be formed but will be less bright
    Correct
  • C
    Two images will be formed
  • D
    No image is formed by the remaining portion of the lens
7
A bird flies down vertically towards a water surface. To a fish inside the water, vertically below the bird, the bird will appear to
  • A
    move slower than its actual speed
  • B
    be closer than its actual distance
  • C
    move faster than its actual speed
    Correct
  • D
    be at its actual distance
8
The layered lens is made of two kinds of glass. A point source of light is placed on its principal axis. If the reflections from the boundaries between layers are ignored, the lens will form
  • A
    infinite images
  • B
    no image at all
  • C
    two images
    Correct
  • D
    only one image
9
Spherical aberration in a thin lens can be reduced by
  • A
    using a monochromatic light
  • B
    increasing the size of the lens
  • C
    using a doublet combination
  • D
    using a circular annular mask over the lens
    Correct
10
In a Young’s double-slit experiment, if the slits are of unequal width
  • A
    fringes will not be formed
  • B
    the positions of minimum intensity will not be completely dark
    Correct
  • C
    bright fringe will not be formed at the centre of the screen
  • D
    distance between two consecutive bright fringes will not be equal to
11
An equi-convex crown glass lens has a focal length 20 cm for violet rays. Its focal length for red rays is \({\mu _{\rm{v}}} = {\rm{1}}.{\rm{5 }}\& {\rm{ }}{\mu _{\rm{r}}} = {\rm{ 1}}.{\rm{47}}\)
  • A
    24.85 cm
  • B
    21.28 cm
    Correct
  • C
    20.82 cm
  • D
    22.85 cm
12
A convex crown glass lens (\({\mu _{\rm{g}}}\) = 1.5 ) has a focal length of 8 cm when placed in air. What is the focal length of the lens when it is immersed in water \(\mu \) w\( < /{\rm{sub}} > {\rm{ }} = {\rm{ 4}}/{\rm{3}})? < \)
  • A
    16 cm
  • B
    8 cm
  • C
    4 cm
  • D
    32 cm
    Correct
13
The equi-convex lens, show in the figure, has a focal length ƒ. What will be the focal length of each half if the lens it cut along AB?
Question 13 figure 1
  • A
    ƒ
  • B
    3 ƒ /2
  • C
    ƒ /2
  • D
    2 ƒ
    Correct
14
A person can see clearly only up to a distance of 30 cm. He wants to read a book placed at a distance of 50 cm from his eyes. What is the power of the lens he requires for his spectacles?
  • A
    -1.67 D
  • B
    -2.0 D
  • C
    -1.0 D
  • D
    -1.33 D
    Correct
15
A person with defective eyesight is unable to see objects clearly nearer than 1.5 m. He wants to read a book placed at a distance of 30 cm from his eyes. Find the power of the lens he requires for his spectacles
  • A
    + 2.67 D
    Correct
  • B
    + 2.5 D
  • C
    -2.67 D
  • D
    -2.5 D