Question

where should an object be kept in the principle axis of a convex lens of focal length 10cm, in orders to get image which is double the size of the obect?

Answer 1

i think object should be placed on its place

Answer 2

f = -10cm

m= 2

m= v/u

2u= v------[1]

1/f= 1/v - 1/u

1/10 = 1/2u - 1/u.       from 1

1/10 = 1-2/ 2u

2u = -10

u = 5cm in front of the lens