A ray of light moves from a rarer medium to a denser medium as shown in the diagram given below: 
Write down the number of the ray which represents the partially reflected ray.
Ray 2
i) What is meant by the term critical angle?
ii) How is it related to the refractive index of the medium?
iii) Does the depth of a tank of water appear to change or remain the same when viewed normally from above?
i)
Critical angle: It is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 90o.
ii)
= cosec ic, where ic is the critical angle.
where, ic is the critical angle.
iii)
When viewed from above, the apparent depth appears to change (decreases).
But, in reality, actual depth = apparent depth and hence, there is no change in the depth.
A ray of light PQ is incident normally on the hypotenuse of a right-angled prism ABC as shown in the diagram alongside:
i) Copy the diagram and complete the path of the ray PQ till it emerges from the prism?
ii) What is the value of the angle of deviation of the ray?
iii) Name an instrument where this action of the prism is used?
i)
The path of the ray PQ till it emerges from the prism is as shown below: 
ii)
Angle of deviation = 180o
iii)
Prism binocular
In the diagram below, PQ is a ray of light incident on a rectangular glass block.
i) Copy the diagram and complete the path of the ray of light through the block. In your diagram, mark the angle of incidence by letter ‘I’ and the angle of emergence by the letter ‘e’.
ii) How are the angles ‘I’ and ‘e’ related to each other? [2]
i)
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