Question

An object is placed at a distance of 50 cm from a concave lens of focal length 20 cm . find the nature and position of the image

Answer 1

object distance is given = - 50 cm
focal length = - 20. find the image distance if the image distance is + then it form virtual and erect image if it is - then it form real and inverted image + front - behind

Answer 2

Explanation:

The nature and approximate position is trivial. Concave lenses always produce virtual, upright, reduced images closer to the lens than the object.

Use the Lens Formula (here with Real Is Positive convention)

• 1/v + 1/u = 1/f
• 1/v = 1/f - 1/u = -1/30 - 1/50 = -5/150 - 3/150 = -8/150

• v = -150/8 or 18.75 from the lens, virtual.

• M = v/u = -150/8 / +50 = -3/8

(Negative here indicates erect image)