A plano convex lens has focal length f = 20 cm. If its curved surface is silvered, then the new focal length will be (refractive index = 1.5) (1) 20 cm (2) 5/3 cm (3) 10/3 cm (4) 25/3 cm?
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Solution:
The focal length of the plano - convex lens is 20 cm with the plane surface being silvered.
So, the net power of the lens is given by
P = 1/f × 2 = 2/f
So, the net focal length is = f/2
=> f/2 = 20
=> f = 20/2
=> f = 10
Thus, the net focal length = 10
The focal length of the plano - convex lens is 20 cm with the plane surface being silvered.
So, the net power of the lens is given by
P = 1/f × 2 = 2/f
So, the net focal length is = f/2
=> f/2 = 20
=> f = 20/2
=> f = 10
Thus, the net focal length = 10
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