Question

answer this..........

Answer 1

hey mate!

in 3rd situation the object is at -40 and the image if +40 , this case can be only when the object is at 2f1 and image is also at 2f2

thus 2f=-40
so, f=-40/2=-20

(1)and (4) observation is not correct as the postion of image is not correct, in (1) the position of the image should be at focus but it is between 2f1 and 2f2 and in (4) the image should be between f1 and 2f1 but is beyond 2f2 .

hope it helped!