Question

Calculate the focal length when object distance is 30 and image distance is 30

Answer 1

for lens :-

u=-30 (from sign conversion of lens)

v=30

1/f=1/v-1/u

1/f =1/30 - (1/-30)

1/f = 1/30 +1/30

1/f= 2/30

f=15 units .