Geometrical OpticsEasy

Question

A concave lens of glass, refrective index 1.5 has both surfaces of same radius of curvature R. On immersion in a medium of refractive index 1.75, it will behave as a

Options

A.convergent lens of focal length 3.5 R
B.convergent lens of focal length 3.0 R
C.divergent lens of focal length 3.5 R
D.divergent lens of focal length 3.0 R

Solution

        
R1 = - R, R2 = + R, μg = 1.5 and μm = 1.75
∴    
Substituting the values, we get
       
        =
∴     f = 03.5R
Therefore, in the medium it will behave like a convergent lens of focal length 3.5 R. It can be understood as μm > μg, the lens will change its behaviour.

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