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QNEET-2021-Ph-648: NEET 2021 Physics - Class 12 NEET-2021-Ph-648 Solution: A point object is placed at a distance of 60 cm from a convex…
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 - 20 cm from the plane mirror it would be a virtual image. 20 cm from the lens it would be a real image. 30 cm from the lens it would be a real image. 30 cm from the plane mirror it would be a virtual image.
Multiple Choice Options
- A 20 cm from the plane mirror, it would be a virtual image.
- B 20 cm from the lens, it would be a real image.
- C 30 cm from the lens, it would be a real image.
- D 30 cm from the plane mirror, it would be a virtual image.
Step-by-Step Verified Solution
First for image formation from lens
u = _ 60 cm
f = +30 cm
_ v = u f u + f = _ 60 _ 30 _ 60 + 30 = 60 cm
This real image formed by lens acts as virtual object for mirror.
Real image from plane mirror is formed 20 cm in front of mirror, hence at 20cm distance from lens. Now for second refraction from lens,
u = _ 20 cm
f = +30 cm
v = u f u + f = _ 20 _ 30 _ 20 + 30 = _ 60 cm
So, final virtual image is 60 cm from lens, or 20 cm behind mirror.