Q. 265.0( 2 Votes )

Find the focal le

Answer :

The experimental setup is used to determine the focal length of a concave mirror. The focal length is just the distance between the mirror and the point where all the parallel rays meet after reflection. So, the calculations are,

f (focal length) = (mark at which is mirror is placed) – (mark at which is screen is placed) {as shown in the diagram}

f= 33.6 – 22.6 = 11 units.

So, the focal length of the given spherical mirror is 11 units.


If we compare air and glass, air is optically rarer medium. And we know that, when a ray of light enters an optically denser medium from an optically rarer medium, light ray bends towards the normal.

Here, the angle of incidence = 60°

The light ray will bend towards normal, and hence, the angle of refraction will be less than the angle of incidence.

The angle of incidence > angle of refraction.

Therefore, the angle of refraction could be 42°and not 65°.

Hence, reading recorded by student P is correct.

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