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JEE Main20264 April 2026Morning ShiftPhysicsRay OpticsActual

A rod of length 10 cm lies along the principle axis of a concave mirror of focal length 10 cm as shown in figure. The length of the image is _____ cm.

Options

  1. A2.5
  2. B5
  3. C7.5
  4. D7

Correct answer

B. 5

Step-by-step solution

For the given concave mirror, the focal length is f = -10 cm. The rod lies along the principal axis. From the figure, the near end of the rod is at a distance of 20 cm from the pole of the mirror. Since the length of the rod is 10 cm, the far end is at a distance of 20 + 10 = 30 cm from the pole. Let the near end be A and the far end be B . Object distance for end A , u_A = -20 cm. Object distance for end B , u_B = -30 cm. Using the mirror formula, 1 v + 1 u = 1 f For end A : 1 v_A + 1 -20 = 1 -10 1 v_A = 1 20 - 1

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