Q. 1 M5.0( 1 Vote )
What is the focal length of a convex lens having power + 5.0D?
A. - 10cm
B. - 20cm
C. + 10cm
D. + 20cm
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.
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