Aconverging lens of focal length 20 cm is placed in contact with a diverging lens of focal length 30 cm. the focal length of this combination is

The focal lenth (F) =+10.0cm

Explanation:

The formular for combined focal length (F) is given as;

In this  question,

F1 = 20cm

F2  = -30cm

Plugging the values into the formuar above,

f = 58.82cm

i.e. the combination behaves as a converging lens (because of the postive sign) of focal length 58.82cm .

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