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Concepts Of Physics MCQ Edition [Volume 1]PhysicsGeometrical Optics

A 5 mm high pin is situated at a distance of 15 cm from a convex lens of focal length 10 cm . Positioned 40 cm from the first lens and 55 cm from the pin is a second lens having a focal length of 5 cm . Identify the nature of the final image.

Options

  1. AInverted and virtual
  2. BErect and real
  3. CInverted and real
  4. DErect and virtual

Correct answer

B. Erect and real

Step-by-step solution

For the first lens: 1 v₁ - 1 u₁ = 1 f₁ 1 v₁ - 1 -15 = 1 10 1 v₁ = 1 10 - 1 15 = 1 30 v₁ = 30 cm Magnification of the first lens, m₁ = v₁ u₁ = 30 -15 = -2 The image formed by the first lens acts as the object for the second lens. The distance between the lenses is 40 cm . Object distance for the second lens, u₂ = -(40 - 30) = -10 cm For the second lens: 1 v₂ - 1 u₂ = 1 f₂ 1 v₂ - 1 -10 = 1 5 1 v₂ = 1 5 - 1 10 = 1 10 v₂ = 10 cm Since v₂ is positive, the final image is real. Magnification of the second lens, m₂ = v₂ u₂

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