Physics
In the figure, PQ and PR are the two light rays emerging from an object P. The ray PQ is refracted as QS.
(a) State the special name given to the angle of incidence ∠PQN of the ray PQ.
(b) What is the angle of refraction for the refracted ray QS?
(c) Name the phenomenon that occurs if the angle of incidence ∠PQN is increased.
(d) The ray PR suffers partial reflection and refraction on the water-air surface. Give reason.
(e) Draw in the diagram the refracted ray for the incident ray PR and hence show the position of image of the object P by the letter P' when seen vertically from above.
Refraction Plane Surfaces
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Answer
(a) The angle of incidence ∠PQN is known as the critical angle.
(b) For the refracted ray QS, the angle of refraction is 90°.
(c) When the angle of incidence ∠PQN is increased, then the phenomenon that occurs is total internal reflection.
(d) For the ray PR, the angle of incidence is less than ∠PQN ( i.e the critical angle ). So according to the laws of reflection, ray PR suffers partial reflection and refraction.
(e) Below diagram shows the refracted ray and the position of image of the object P when seen vertically from above:
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The refractive index of glass is 1.5. From a point P inside a glass slab, draw rays PA, PB and PC incident on the glass-air surface at an angle of incidence 30°, 42° and 60° respectively.
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(Take sin 42° = 2 / 3)