Mayflower Sec Sem 1 2005 P2 Q6
The diagram below shows a long block of glass over an object O. Light from O reaches the top surface of the glass at X, Y and Z. The refractive index of the glass is 1.5.
(a) What is the name given to the bending of light at X?
(b) Calculate angle a.
(c) Calculate angle b.
(d) Explain why the ray at point Z travels in the path as indicated in the diagram.
(e) Calculate angle c.
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Answer:
(a) Refraction
(b) refractive index = sin a / sin (90° - 60°)
sin a = 1.5 * sin 30°
sin a = 0.75
a = 48.6°
(c) angle b is critical angle
Hence,
refractive index = 1 / sin b
sin b = 1 / 1.5
sin b = 2/3
b = 41.8°
(d) Angle c is greater than the critical angle, and since the light ray is moving from a denser medium to a less dense medium, total internal reflection occurs.
(e) c = 70° (reflection)
