Question

a convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses would be:

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Answer 1

Answer:

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Answer 2

Answer:

f1= +10 for convex lens.

f2 =−20cm for concave lens

The focal length of the combination is given by

1/f=1/f2+1/f2

1/f=1/+10cm + 1/-20cm=1/20cm.

f=+20cm