Question

thick convex lens gives the real image of an object magnified 3 times. when the lens is moved 0.1m towards object the image is magnified 5 times. find focal length​

Answer 1

Explanation:

u=20cm

m=1/0=V/U

3=V/20

therefore,V=-20×3

= 60cm behind the lense 1/F=1/V-1/U

=-1/60 -(-1/20

(-1+3)/60

2/60

as1/F=2/60

therefore F=60/2=30cm