What is the focal length of a convex lens of focal length `30 cm` in contant with a concave lens of focal length `20 cm`. Is the system a converging or a diverging lens ? Ignore thickness of the lenses.
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Here, `f_(1) = 30 cm, f_(2) = - 20 cm, f = ?` As `(1)/(f) = (1)/(f_(1)) + (1)/(f_(2)) :. (1)/(f) = (1)/(30) - (1)/(20) = (2 - 3)/(60) = -(1)/(60)` `:.` The combination of lenses behave as a concave lens. The system is not converging.
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