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
Magnifying power of a compound microscope is high if
  • A
    both objective and eye-piece have short focal lengths
    Correct
  • B
    the objective has a long focal length and eye-piece has a short focal
  • C
    the objective has a short focal length and the eye-piece has a long
  • D
    both objective and eye-piece have long focal lengths
2
The magnifying power of telescope is high if
  • A
    the objective has a short focal length and the eye-piece has a long focal length
  • B
    both objective and eye-piece have short focal lengths
  • C
    the objective has a long focal length and the eye-piece has a short focal length
    Correct
  • D
    both objective and eye-piece have long focal length
3
A lens of power + 2.0 D is placed in contact with another lens of power – 1.0 D. The combination will behave like
  • A
    a diverging lens of focal length 100 cm
  • B
    a diverging lens of focal length 50 cm
  • C
    a converging lens of focal length 100 cm
    Correct
  • D
    a converging lens of focal length 50 cm
4
A parallel beam of light falls on a convex lens. The path of the rays is shown in the following figure. It follows that
Question 4 figure 1
  • A
    \({\mu _{\rm{1}}} < {\rm{ }}\mu {\rm{ }} < {\rm{ }}{\mu _{\rm{2}}}\)
  • B
    \({\mu _{\rm{1}}} > {\rm{ }}\mu {\rm{ }} > {\rm{ }}{\mu _{\rm{2}}}\)
  • C
    \({\mu _{\rm{1}}} = {\rm{ }}\mu {\rm{ }} < {\rm{ }}{\mu _{\rm{2}}}\)
    Correct
  • D
    \({\mu _{\rm{1}}} = {\rm{ }}\mu {\rm{ }} > {\rm{ }}{\mu _{\rm{2}}}\)
5
To print a photograph from a negative, the time of exposure to light from a lamp placed 60 cm away is 2.5 s. What exposure time is required if the lamp is placed 1.2 m away?
  • A
    5 s
  • B
    15 s
  • C
    20 s
  • D
    10 s
    Correct
6
The diameter of a plano-convex lens is 6 cm and the thickness at the centre is 3 mm. If the speed of light in the material of the lens is \({\rm{2 }} \times {\rm{ 1}}{0^{\rm{8}}}{\rm{m}}{{\rm{s}}^{ - {\rm{1}}}}\) the focal length of the lens is
  • A
    15 cm
  • B
    10 cm
  • C
    20 cm
  • D
    30 cm
    Correct
7
A plano-convex lens, when silvered on the plane side, behaves like a concave mirror of focal length 30 cm. When it is silvered on the convex side, it behaves like a concave mirror of focal length 10 cm. The refractive index of the material of the lens is
  • A
    3.0
  • B
    2.5
  • C
    2.0
  • D
    1.5
    Correct
8
A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screen
  • A
    complete image will be formed
    Correct
  • B
    none of these
  • C
    half the image will disappear
  • D
    intensity of the image will increase
9
When a ray of light enters a glass slab from air
  • A
    its frequency increases
  • B
    neither wavelength nor frequency changes
  • C
    its wavelength increases
  • D
    its wavelength decreases
    Correct
10
In a compound microscope, maximum magnification is obtained when the final image
  • A
    is formed at infinity
  • B
    coincides with the object
  • C
    coincides with the objective
  • D
    is formed at the least distance of distinct vision
    Correct
11
A spherical surface of radius of curvature R separates air (refractive index from glass (refractive index 1.5 ). The centre of curvature is in the glass. A point object P placed in air is found to have a real image Q in the glass. The line PQ cuts the surface at point O and PO = OQ. The distance PO is equal to
  • A
    1.5 R
  • B
    5 R
    Correct
  • C
    2 R
  • D
    3 R
12
A eye specialist prescribes spectacles having a combination of a convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. The power of this combination is
  • A
    + 6.67 D
  • B
    -1.5 D
    Correct
  • C
    + 1.5 D
  • D
    -6.67 D
13
A concave lens of glass, refractive index 1.5, has both surfaces of the same radius of curvature R. On immersion in a medium of refractive index 1.75, it will behave as a
  • A
    convergent lens of focal length 3.5 R
    Correct
  • B
    divergent lens of focal length 3.0 R
  • C
    convergent lens of focal length 3.0 R
  • D
    divergent lens of focal length 3.5 R
14
According to Cartesian sign convention.
  • A
    None of the above
  • B
    Distances measured behind the pole direction are taken as positive
  • C
    Distances measured in the same direction as the incident light are taken as negative
  • D
    Distances measured in the same direction as the incident light are taken as positive
    Correct
15
Domestic power supply in India is
  • A
    90 cm, 10 cm
  • B
    50 cm, 50 cm
  • C
    96 cm, 4 cm
    Correct
  • D
    80 cm, 20 cm