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

- 10 cm

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- 20 cm

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+ 10 cm

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+ 20 cm

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Solution

The correct option is D + 20 cm
+ 20 cm
Power (in D) = $\frac{1}{f (i n m)}$
$∴ f = \frac{1}{5} = 0.2 m = 20 c m$

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Similar questions

Q. A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:
(a) +10 cm
(b) +20 cm
(c) −10 cm
(d) −20 cm

Q. The focal lengths of four convex lenses P, Q, R and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. The lens having greatest power is :
(a) P
(b) Q
(c) R
(d) S

For an object placed at a distance 20 cm in front of a convex lens, the image is at a distance 20 cm behind the lens. The focal length of convex lens is :

(a) 20 cm (b) 10 cm (c) 15 cm (d) 40 cm

Q. To obtain a magnification of, –2 with a convex lens of focal length 10 cm, the object should be placed:
(a) between 5 cm and 10 cm
(b) between 10 cm and 20 cm
(c) at 20 cm
(d) beyond 20 cm

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

The correct option is D + 20 cm+ 20 cmPower (in D) = 1f(in m)∴f=15=0.2 m=20 cm

The correct option is D + 20 cm
+ 20 cm
Power (in D) = $\frac{1}{f (i n m)}$
$∴ f = \frac{1}{5} = 0.2 m = 20 c m$