Which of the following statements is true?
(a) A convex lens has 4 dioptre power having a focal length 0.25 m
(b) A convex lens has –4 dioptre power having a focal length 0.25 m
(c) A concave lens has 4 dioptre power having a focal length 0.25 m
(d) A concave lens has –4 dioptre power having a focal length 0.25 m
Answer
- A convex lens has
- a positive focal length ( 0.25m)
- and hence would also have a positive power (+4D).
- A concave lens has
- negative focal length (-0.25m)
- and hence has negative power ( -4D)
So, the correct
answer is (a)
