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प्रश्न
Which of the following statements is true?
पर्याय
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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