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A person can see distinctly any object s...

A person can see distinctly any object situated in between the distance 50 cm and 300 cm. what type of spectacles are to used (ii) to bring the least distance of distinct vision at 25 cm ? What will be the rangs of distinct vision in each pair of spectacles?

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To bring the near point to 25 cm from 50 cm spectacles with convex lens are to be used. Here, u=-25 cm and v=-50 cm .
So from the equation `1/v-1/u=1/f` we have ,
`1/f=-1/(50)-1/(-25)=1/(50) or , f=50 cm `
So a convex lens of focal length 50 cm is to be used. To find out the point v=-300 cm ,f=50 cm ,u=?
`therefore 1/(-300)-1/u=1/(50) or, 1/u =1/(-300)-1/(50)-7/(300) or, u=(-300)/7=-42.86 cm `
In this case the range of vision of the man extends from 25 cm to 42.86 cm.
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