Question

deduce the equivalent focal length of two convex lenses of focal lengths F1 and F2 when placed in contect.​

Answer 1

⭐Solution⭐

Since the lens addition formula adds the reciprocal of the component focal lengths, the resulting focal length will be 1/2 the original focal length.

Since the lens addition formula adds the reciprocal of the component focal lengths, the resulting focal length will be 1/2 the original focal length.Here's the break down :

$\frac{1}{f} = \frac{1}{ f_{1} } + \frac{1}{ f_{2} } \\ where. \: f_{1} = f_{2} \\ \frac{1}{f} = \frac{1}{ f_{1} } + \frac{1}{ f_{2} } = \frac{2}{ f_{1} } \\ so. \: f = \frac{ f_{1} }{2}$

similarly, if three lenses were placed in contact, then the combined focal length would be 1/3 of a single lens.

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