Physics

CBSE Class 12

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31.

A point object 'O' is kept in a medium of refractive index *n*_{1} in front of a convex spherical surface of radius of curvature *R* which separates the second medium of refractive index *n*_{2} from the first one, as shown in the figure.

Draw the ray diagram showing the image formation and deduce the relationship between the object distance and the image distance in terms of *n*_{1}, *n*_{2} and *R*.

b) When the image formed above acts as a virtual object for a concave spherical surface separating the medium *n*_{2} from *n*_{1} (*n*_{2} > *n*_{1)}, draw this ray diagram and write the similar (similar to (a)) relation. Hence obtain the expression for the lens maker’s formula.

Ray diagram showing the image formation is given below:

The rays are incident from medium of refractive index n_{1} to another medium of refractive index n_{2.}

NM is taken to be nearly equal to the length of the perpendicular from the point N on the principal axis.

We can have approximation for small angles. We get,

b)

When the image formed is virtual and n_{2} > n_{1}

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