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

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments1 Mark
Question
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: Optical fibers are used to transmit light without any loss in its intensity over distance of several kilometers. Reason: Optical fibers are very thick and all the light is passed through it without any loss.
✓

Answer

  1. A is true but R is false.
Explantion:
Optical fiber is extremely thin (radius of few microns) and long strand of very fine quality glass or quartz. When tight is incident at a small angle at one end, it gets refracted into the strands (or fibres) and incident on the interface of the fibres and the coating. The angle of incidence being greater than the critical angle, the ray of light undergoes total internal reflections. It suffers the internal reflection again and again, till the angle of incidence remains greater than the critical angle for fibre material with respect to coating. Due to successive total internal reflection there is no loss of intensity in optical fibres.

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