A man wishes to view an object through a convex lens of focal length 10cm. The final image is to be eret and magnified 2 times. How far from the object must he hold the lens?

Explanation

Here, `f=+10 cm ` and `m=+2` (Magnification is now positive as the image is erect. ) Let the object distace from the lens be x.
Then `u=-x` and `v=m u=2x`
Substituting in equation, we get
`(1)/(10)=(1)/(-2x)-(1)/(-x)` or `x=5cm`
Therefore, the lens is to be held 5 cm from the object.