Two lenses have powers equal to +2 D and -4 D from Class Physics Ray Optics and Optical Instruments

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CBSE

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Physics
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NEET Physics : Ray Optics and Optical Instruments

Multiple Choice Questions

151.

To get three images of a single object, one should have two plane mirrors at an angle of

  • 60°

  • 90°

  • 120°

  • 30°



152.

The magnification of an astronomical telescope is 10 and the focal length of eye-piece is 20 cm. The focal length of objective lens is

  • 1200 cm

  • 2 cm

  • 200 cm

  • 100 cm



153.

Two lenses have powers equal to +2 D and -4 D respectively, the power of combination will be

  • -2D

  • +2D

  • -4D

  • +4D



154.

The colour of a red cloth in green light appears

  • red

  • green

  • orange

  • black



155.

A convex lens of focal length 12 cm is made up of a glass of refractive index 32.When it is immersed in a liquid of refractive index 54, its focal length will be

  • 15 cm

  • 6 cm

  • 30 cm

  • 24 cm



156.

When a ray is incident on a medium of refractive index n at Brewster's angle,it gets

  • totally reflected

  • totally absorbed

  • circularly polarised

  • plane polarised



157.

Consider telecommunication through optical fibres. Which of the following statements is not true?

  • Optical fibres can be of graded refractive index

  • Optical fibres are subjected to electromagnetic interference from outside

  • Optical fibres have extremely low transmission loss

  • Optical fibres may have homogeneous core with a suitable cladding



158.

A diver, at a depth of 12 metre from the surface of the water, sees the sky within a cone whose half vertex angle is : aμw=43

  • cos−143

  • sin−143

  • 90°

  • sin−134



159.

Focal length of a lens is +10 cm and its refractive index is 1.4, it is dipped in a liquid of refractive index 1.6, then its focal length becomes

  • - 16 cm

  • + 32 cm

  • + 16 cm

  • - 32 cm



160.

An astronomical telescope has a large aperture to

  • reduce spherical aberration

  • have high resolution

  • increase span of observation

  • have low dispersion



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