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Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments1 Mark
MCQ

Consider an extended object immersed in water contained in a plane trough. When seen from close to the edge of the trough the object looks distorted because:

  • A
    The apparent depth of the points close to the edge are nearer the surface of the water compared to the points away from the edge.
  • B
    The angle subtended by the image of the object at the eye is smaller than the actual angle subtended by the object in air.
  • C
    Some of the points of the object far away from the edge may not be visible because of total internal reflection.
  • D
    Water in a trough acts as a lens and magnifies the object.
✓

Answer

  1. The apparent depth of the points close to the edge are nearer the surface of the water compared to the points away from the edge.
  2. The angle subtended by the image of the object at the eye is smaller than the actual angle subtended by the object in air.
  3. Some of the points of the object far away from the edge may not be visible because of total internal reflection.

Solution:

Key concept: The light from the pencil is refracted when it passes from the water into air, bending away from the normal as it moves from high to low refractive index.

When light from the submerged object before reaching to the observer gets, refracted from water surface, the rays bend away from normal and the angle subtended by the image of the object at the eye is smaller than the actual angle subtended by the object in air. Also the apparent depth of the .points close to the edge are nearer the surface of the water compared to the points away from the edge.

As we move towards right, the angle of incident increases and becomes equal to critical angle. Hence some of the points of the object far away from the edge may not be visible because of total internal reflection.

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