Question

object is placed at 30 cm from a convex lens and its real image formed at 20 cm away from a lens .calculate focal length of convex lens . Draw rag diangram

Answer 1

As u=30 & v=20 given

Put the formula of focal lenth

1/f = 1/u+1/v

1/f = 1/30 + 1/20

1/f = 2 + 3 /60  

1/f = 5/60

1/ f = 12cm

F= 12 cm

Hope so its clear to u