JEE Main 2026 Apr 5 Shift 2, Physics Q15: Thin Lens and Mirrors

JEE Main2026Apr 5, Shift 2Physics

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?

A
behaves as concave lens if $∣ f_{convex} ∣ > ∣ f_{concave} ∣$
B
behaves as concave lens if $∣ f_{convex} ∣ < ∣ f_{concave} ∣$
C
behaves as convex lens if $∣ f_{convex} ∣ > ∣ f_{concave} ∣$
D
Focal length of the lens system will change if the position of two lenses are interchanged

Solution

For thin lenses in contact, $\frac{1}{f} = \frac{1}{f _{1}} + \frac{1}{f _{2}}$ . Taking $f_{1} = + ∣ f_{convex} ∣$ and $f_{2} = - ∣ f_{concave} ∣$ :

$\frac{1}{f} = \frac{1}{∣ f _{convex} ∣} - \frac{1}{∣ f _{concave} ∣}$ .

If $∣ f_{convex} ∣ > ∣ f_{concave} ∣$ , the first term is smaller in magnitude, so $1/ f < 0$ , meaning the combination is concave (diverging).

The focal length is symmetric in the two lenses, so swapping their positions does not change $f$ .

Concept behind this question

Thin Lens and MirrorsNotes, formulas and examples →

Practice more Physics

Concept-wise practice with instant solutions on Fundamenthol.

Start practicing →

JEE Main 2026 Apr 5 Shift 2, Physics Q15: Thin Lens and Mirrors

Concept behind this question

More previous year questions on Thin Lens and Mirrors

Practice more Physics