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A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also find the power of the lens.

 A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also find the power of the lens.

Grade:12

1 Answers

Harshit Singh
askIITians Faculty 5963 Points
3 years ago
Dear Student

Object distance, u= – 50 cm
Image distance, v= 50 cm
Focal length = f
According to the lens formula,
u = -50 cm v = + 50 cm.
f =?
1/f = 1/v – 1/u
1/f = 1/50 + 1/50
f = + 25 cm. = 0.25 m
Power of lens (P) = 1/f = 1/ 0.25 = + 4D.

Thanks

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