JEE Main 2026 · 5 Apr · Shift 2 · Physics Q40

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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 ?

behaves as concave lens if

|f_{\text{convex}}|>|f_{\text{concave}}|

behaves as concave lens if

|f_{\text{convex}}|<|f_{\text{concave}}|

behaves as convex lens if

|f_{\text{convex}}|>|f_{\text{concave}}|

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

Answer and worked solution

Official answer: A

Lenses in contact.
$\frac1F=\frac1{|f_{\text{convex}}|}-\frac1{|f_{\text{concave}}|}.$

When it diverges. F is negative (a concave combination) when $|f_{\text{convex}}|>|f_{\text{concave}}|$ , which is option (A). Option (C) gets the inequality backwards. Thin lenses in contact give the same F in either order, so (D) is false.

(A)

Topics:Combination of lenses and mirrors

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JEE Main 2026 · 5 Apr · Shift 2, Physics question 40