A convex lens of focal length $30 c m$ is placed coaxially in contact with a concave lens of focal length $40 c m$ . Determine the power of the combination. Will the system be converging or diverging in nature?

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Solution

Since, $P = \frac{1}{f} = \frac{1}{f o c a l l e n g t h}$

$P =$ Power of the lens.

$f_{1} = 30 c m = \frac{30}{100} m$

$P_{1} = \frac{100}{30} = + 3.3 d i o p t e r$

$f_{2} = 40 c m = \frac{40}{100} m$

$P_{2} = \frac{100}{- 40} = - 2.5 d i o p t e r$

So $P_{t o t a l} = + 3.3 - 2.5 = 0.8 d i o p t e r$

It acts as convex lens.

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A convex lens of focal length 30cm is placed coaxially in contact with a concave lens of focal length 40cm. Determine the power of the combination. Will the system be converging or diverging in nature?

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