Question

A person has least distance of distinct vision of 75 cm . What should be the focal length of the lens that is required for him to read a news paper at a distance of 45cm ?
No rubbish answer ..

Answer 1

Hey mate ! ( No rubbish answer here)

The person near point is 75 cm , i.e, he could not see objects near than 75 cm . This defect is called hypermetropia and this can be rectified using convex lens .

1/f = 1/v - 1/u

u = -25 cm = -0.25 m

Hence , v= -75 cm = 0.75

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Answer 2

Answer:

Focal length of the lens will be equal to 37.5cm

Explanation:

We have given that the least distance of vision for a person is 75 cm

So u = 75 cm

To read the book image should be formed at a distance of v = 25 cm

We have to fond the focal length of the lens

For lens we know that , here v is image distance and u is object distance

So  

f = 37.5 cm

So focal length of the lens will be equal to 37.5 cm

HOPE IT HELPS U!!!

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