A thin convex lens and a thin concave lens are kept in contact and are co-axial. Which of the following

Question

A thin convex lens and a thin concave lens are kept in contact and are co-axial. Which of the following statements is correct for this combination of two lenses? [2026]

Smart Achievers · Accepted Answer

(1)

$\frac{1}{f_{e q}} = \frac{1}{f_{c o n v e x}} + \frac{1}{f_{c o n c a v e}}$

$f_{c o n c a v e} is -ve$

$f_{c o n v e x} is +ve$

$If$ $| f_{c o n c a v e} |$ $<$ $| f_{c o n v e x} |$

$then, f_{e q} is negative.$

Solution

Q.
A thin convex lens and a thin concave lens are kept in contact and are co-axial. Which of the following statements is correct for this combination of two lenses [2026]

1 behaves as concave lens if $| f_{convex} |$ $>$ $| f_{concave} |$

2 behaves as concave lens if $| f_{convex} |$ $<$ $| f_{concave} |$

3 behaves as convex lens if $| f_{convex} |$ $>$ $| f_{concave} |$

4 Focal length of the lens system will change if the position of two lenses are interchanged

Ans.
(1)

$\frac{1}{f_{e q}} = \frac{1}{f_{c o n v e x}} + \frac{1}{f_{c o n c a v e}}$

$f_{c o n c a v e} is -ve$

$f_{c o n v e x} is +ve$

$If$ $| f_{c o n c a v e} |$ $<$ $| f_{c o n v e x} |$

$then, f_{e q} is negative.$

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Solution

Q. A thin convex lens and a thin concave lens are kept in contact and are co-axial. Which of the following statements is correct for this combination of two lenses [2026]

1 behaves as concave lens if |fconvex|>|fconcave|

2 behaves as concave lens if |fconvex|<|fconcave|

3 behaves as convex lens if |fconvex|>|fconcave|