Same chapter3 marksDifficulty: Medium
Why does a coin at the bottom of a beaker of water appear to be raised?
Refraction of Light at Plane Surfaces
3 marksDifficulty: Medium
Explain how total internal reflection makes an optical fibre able to carry light round bends.
Original Khojo Papers practice question — not from a past board paper.
Answer
Light entering the fibre strikes the boundary between the denser core and the rarer cladding at an angle greater than the critical angle, so none of it escapes and all of it is reflected back into the core. This happens repeatedly along the fibre, so the light follows the fibre even where it bends.
No citable source has been recorded for this record. Treat it as practice material, not as fact.
Explanation
Because no light is lost by refraction at the wall, the signal can travel long distances with little loss.
Related questions
From the same topic and chapter, at a similar level.
Same chapter3 marksDifficulty: Medium
A ray of light travelling in air strikes a glass surface at an angle of incidence of 60°. If the refractive index of glass is 1.5, find the sine of the angle of refraction.
Refraction of Light at Plane Surfaces
Same chapter3 marksDifficulty: Medium
The critical angle for a certain medium is 30°. Calculate its refractive index.
Refraction of Light at Plane Surfaces
Same chapter3 marksDifficulty: Medium
State the two conditions necessary for total internal reflection to take place.
Refraction of Light at Plane Surfaces
Same chapter3 marksDifficulty: Medium
The refractive index of glass is 1.5 and the speed of light in vacuum is 3 × 108 m s−1. Calculate the speed of light in glass.
Refraction of Light at Plane Surfaces
Same chapter3 marksDifficulty: Medium
A tank is filled with water to a depth of 40 cm. If the refractive index of water is 4/3, find the apparent depth of the tank.
Refraction of Light at Plane Surfaces