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  • A convex lens of focal length  and a concave lens of focal length <img alt="\mathrm{y}" src="http

A convex lens of focal length \mathrm{x} and a concave lens of focal length \mathrm{y}are placed in contact. The focal length of the combination is:

Option: 1

\mathrm{(x+y)}


Option: 2

\mathrm{(x-y)}


Option: 3

\mathrm{\frac{xy}{y-x}}


Option: 4

\mathrm{\frac{xy}{y+x}}


Answers (1)

best_answer

The focal length of combination is
\mathrm{\begin{aligned} & \mathrm{\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}=\frac{1}{x}-\frac{1}{y}=\frac{y-x}{x y}} \\ &\mathrm{ f=\frac{x y}{y-x}} \end{aligned}}

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Ritika Jonwal

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