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प्रश्न
Which of the following statements is true?
विकल्प
A convex lens has 4 dioptre power having a focal length 0.25 m
A convex lens has –4 dioptre power having a focal length 0.25 m
A concave lens has 4 dioptre power having a focal length 0.25 m
A concave lens has –4 dioptre power having a focal length 0.25 m
उत्तर
A convex lens has 4 dioptre power having a focal length 0.25 m
Explanation -
The focal length and the power of concave lens is always negative and of convex lens is positive. The relation between power and focal length is, `"P" = 1/"f"`
Using this formula to find power,
`"P" = 1/"f"`
`= 1/0.25`
= 4D
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संबंधित प्रश्न
In order to obtain a real image twice the size of the object with a convex lens of focal length 15 cm, the object distance should be:
(a) more than 5 cm but less than 10 cm
(b) more than 10 cm but less than 15 cm
(c) more than 15 cm but less than 30 cm
(d) more than 30 cm but less than 60 cm
An object 4 cm high is placed at a distance of 10 cm from a convex lens of focal length 20 cm. Find the position, nature and size of the image.
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.
What would be the image distance if the object distance was 90 cm?
What type of images can a convex lens make?
What kind of lens is used to correct
long-sightedness?
A convex lens is placed in water. Its focal length will ______.
Point out the difference between a convex lens and a concave lens.
Where should an object be placed in front of a convex lens so as to form an inverted and enlarged image? Will the image be real or virtual? Draw a ray diagram to illustrate your answer.
Find the odd one out and give its explanation.
Distinguish between:
Concave lens and Convex lens
