Question

an object is placed in front of a coverging lens in such a position that the lens (F=13 cm)creates a real image located 24cm from the lens. then with the object remaining in place ,the lens is replaced with another converging lens (f=17 cm).a new image real image is formed what is the image distance of new image

Answer 1

case-1
   f=13cm    v=24cm     u=?
  1/f=1/v-1/u
1/u=1/v-1/f
1/u=1/24 -1/13
1/u -11/13*24
u= -13*24/11
u=-  28.36cm.
 now for the second condition
f=17cm   u=28.36cm
1/f =1/v-1/u
1/v=1/17 -1/28.36
1/v =11.36/17* 28.36
v=42.44cm
So the new image distance is 42.44 cm