A beam of light converges to a point `P`. A lens is placed in the path of the covergent beam `12 cm` from `P`. At what point does the beam converge if the lens is
(a) a convex lens of focal length `20 cm`
(b) a concave lens of focal length `16 cm` ?

Explanation

To solve the problem, we will use the lens formula:

\[ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \]

where:
- \( f \) is the focal length of the lens,
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