Q. 274.3( 6 Votes )
Angle of incidence is the angle formed between the incident ray and the normal at the air-glass interface.
The angle of refraction is the angle formed between the refracted ray and the normal.
i) When the ray of light travels from rarer medium to denser medium, the speed of the light ray slows down, and hence the ray gets bent towards the normal.
Since the ray of light bends towards the normal, the angle of refraction is less than the incident angle.
So in this case the angle of incidence is greater than the angle of refraction.
ii) For any interface, the angle of emergence is always equal to the incident angle, and hence when we try to increase the angle of incidence, the angle of emergence also increases.
iii) Refraction basically occurs due to the change in the speed of light as the light ray travels from one medium to another of different refractive indices.
So the two where no refraction will take place are as follows:
1. When the incident ray is perpendicular to the medium interface.
2. When the ray of light travels from one medium to another of same refractive indices.
(i) The mirror is a concave mirror as the concave mirrors are only depressed at the centre and the image formed is erect and enlarged which is normally formed by concave mirrors only.
The focal length of the mirror can be determined as follows:
The distance at which the image is formed = 35 cm
The distance at which the mirror is placed = 15 cm.
Focal Length, F = 35 – 15
= 20 cm.
(ii) The main reason for the sharp image of the distant building is that the incident rays from the object are parallel to each other and after being reflected from the concave mirror, the rays converge at the focus on the principal axis.
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