What is the focal length of a convex lens having power + 5.0D?

Power of lens = .

⇒ Focal length =

1m = 100 cm.

⇒ 0.2 m = 0.2 × 100 = 20 cm.

∴ Focal length = 20 cm. (Positive for convex lens.)

Option (A): since focal length is positive for convex lens. Therefore, Option A is incorrect.

Option (B): since focal length is positive for convex lens. Therefore, Option B is incorrect.

Option (C): focal length is 20 cm not 10 cm therefore option (C) is incorrect.

Option (D): as explained in explanation focal length = + 20 cm therefore option D is correct.