Question

one concave and one convex lens both having same focal length 'f' are placed in contact ,then focal length of combination is given by.

a) 0.

b)f/2.

c)f.

d) infinity.

Answer 1

Answer:

Effective focal length in ∞.

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 100fwere 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

hello@

here is u r answer##

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let f be the focal length of combination therefore,

1/f = 1 /f1 + 1/f2


= 1/f - 1/f

= 0

it's means f = infinity.

option (d).


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