Question

calculate the distance at which an object should be placed in front of convex lens of focal length 10cm to obtain a virtual image of double its size b) in above given case find the magnification in image is real express it in terms of relation between v and u​

Answer 1

Answer: u = -5cm

Explanation:

Please refer to the attachment for complete solution and explanation.

Answer 2

The object needs to be placed at a distance of 5cm in front of the convex lens.

f = + 10 cm ( As it is a convex lens) (Given)

m = +2 ( As the image is virtual) (Given)

m = v/u = 2

= 2u

According to the formula of lens -  

1/v - 1/u = 1/f

1/2u - 1/u = 1/10

-1/2u = 1/10

u = -5cm

Therefore, the object needs to be placed at a distance of 5cm in front of the convex lens.