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Light and sound

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Question 50

A light ray can undergo total internal reflection under specific conditions.

a.

Explain what is meant by the term critical angle.

[2]
b.

State two conditions required for total internal reflection to occur.

[2]
c.

The diagram shows a light ray entering a semicircular plastic block and travelling towards the centre point O.

A light ray travels through a semi-circular plastic block from the curved boundary towards the central point O on the flat boundary. A normal line is drawn perpendicular to the flat boundary at point O. The angle of incidence between the ray inside the plastic and the normal is labeled i. Four possible paths for the ray after reaching point O are shown: Path A bends towards the normal in the air; Path B bends away from the normal in the air; Path C travels along the flat boundary; Path D reflects back into the plastic block with an angle equal to i.

The angle of incidence iii is 30∘30^\circ30∘. The critical angle of the plastic is 43∘43^\circ43∘.

(i) Which path does the ray take after reaching point O?

  • A Path A
  • B Path B
  • C Path C
  • D Path D
[2]
d.

State the equation linking critical angle and refractive index.

[1]
e.

Calculate the refractive index of the plastic.

[2]

Light and sound Questions

  1. IGCSE
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  3. /Light and sound