Question

4. Calculate the distance at which an object should be placed in front of a convex lens of focal length 10 cm
to obtain an image of double its size.

Answer 1

given:

v=2u
f=10

using lens formula

1/f=1/v-1/u

1/10=-1/2u-(-1/u)

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

1/10=-1+2/2u

1/10=1/2u

u=5 cm ( answer)