Question

Two lens of power +5d and -10d seperated by 20 cm. What is the equivalent focal length

Answer 1

Answer:

Magnification= v/u =2

v=2u

1/v− /uu = 1/f (Lens formula)

⇒ -1/2u − 1/u= 1/f

⇒u= −f/2= −20/2

=−10cm