Question

An optician prescribes spectacles to a patient with a combination of a convex lens of focal length 40 cm and a concave lens of 25 cm focal length. What will be the power of spectacles?

Answer 1

Answer:

1/F = 1/F1+ 1/F2

1/F = 1/40+1/25

1/F = 65/1000

F = 1000/65

F = 15.38

so the total focal length of lenses is 15.38

power=1/focal length

power=1/15.38

hope it helps