A point object is placed at a distance of 60 cm from a convex lens of focal length 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40 cm from it, the final image would be formed at a distance of :
(1) 20 cm from the lens, it would be a real image.
(2) 30 cm from the lens, it would be a real image.
(3) 30 cm from the plane mirror, it would be a virtual image.
(4) 20 cm from the plane mirror, it would be a virtual image.
Correct answer: (4) 20 cm from the plane mirror, it would be a virtual image.
Explanation:
first, for image formation from lens
u = -60 cm
f = + 30 cm
⇒ v = \(\frac{uf}{u+f}\) = \(\frac{-60 \times 30}{-60 + 30}\) = 60 cm
this real image formed by lens acts as virtual object for mirror