Question

A convex lens of focal length f is put in contact with a
concave lens of same focal length. The focal length of
combination is​

Answer 1

Explanation:

Effective focal length is ∞

.

Explanation:

When two lenses are kept in contact, powers of the lenses are simply added.

Power of a lens is positive for convex lens and negative for concave lens.

Numerically power of a lens is given by

100/f

where , f is focal length in centimeters.

As numerically, focal length is same but opposite in size, combined power will be zero.

i.e. focal length is ∞

i.e. it is just equivalent to plane glass.

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Answer 2

Answer:

Explanation:

The distance between optical centre and principal

focus is called focal length of a lens