1.

A converging lens of focal length 40 cm is kept in contact with a diverging lens of focal length 30 cm. Find the focal length of the combination.

Answer»

\(\frac{1}{F'}= \frac{1}{f_1}+\frac{1}{f_2}\) = \(\frac{1}{+40} +\frac{1}{-30}\) = \(\frac{1}{40}-\frac{1}{30}\)

\(\frac{1}{F'}\) = \(\frac{3-4}{120}\) = \(-\frac{1}{120}cm\)[Diverging]



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