JEE Main 2025 · 2 April · morning · Single correct · +4 / −1

A slanted object A B is placed on one side of convex lens as shown in the diagram. The image is formed on the opposite side. Angle made by the image with principal axis is :

JEE Main PYQ figure
  1. (a) -α
  2. (b) -α/2
  3. (c) -45°
  4. (d) +45°
Answer and solution

Answer (c) -45°

Solution

Physics sir · 4 steps

Image both ends of AB separately with the lens formula, then join them; the slope gives the angle.

  1. Image of A. A is on the axis at u = -30 cm with f = +20 cm. From 1/v - 1/u = 1/f we get 1/v = 1/20 - 1/30 = 1/60, so A' is on the axis at v = 60 cm.
  2. Image of B. B is 1 cm nearer the lens, so u = -29 cm, and it is 2 cm above the axis. Then 1/v = 1/20 - 1/29 = 9/580, so v = 580/9 cm ≈ 64.4 cm.

    m = v/u = (580/9)/-29 = -20/9, h' = 2 × (-20/9) = -40/9 cm

  3. Join the ends. Along the axis, B' is 580/9 - 60 = 40/9 cm beyond A', and it is 40/9 cm below the axis. The slope of A'B' is (-40/9)/(40/9) = -1.
  4. So. The image makes tan⁻¹(-1) = -45° with the principal axis, which is option (c).

The idea to keep. A slanted object is not imaged as a scaled copy, because the lens stretches lengths along the axis differently from heights. Find the image of each end point and join them.

Answer from the NTA final answer key. Solution by PrepWiser.

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Asked about 200 times in JEE Main since 2020. This question is from 2025.