Q90 / 90 · JEE Main 2016 (09 Apr Online) · Physics

A convex lens, of focal length 30 cm, a concave lens of focal length 120 cm, and a plane mirror are arranged as shown. For an object kept at a distance of 60 cm from the convex lens, the final image, formed by the combination, is a real image, at a distance of:

Figure

  • Correct answer
    A
    60 cm from the convex lens
  • B
    60 cm form the concave lens
  • C
    70 cm from the convex lens
  • D
    70 cm from the concave lens

Solution

From lens formula for convex lens, we have
1f=1v-1u
⇒130=1v+160
⇒160=1v

Applying lens formula to concave lens, we have 
1f=1v-1u
⇒1-120=1v-140, ∵u=+40 cm
⇒v=60 cm

Virtual object 10 cm behind plane mirror.
Hence real image 10 cm in front of mirror.
Hence 60 cm from convex lens.

Hence, the correct answer is option: 'A'.

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