Calculate the focal length of a reading glass of a person, if the distance of distinct vision is 75cm.
Calculate the focal length of a reading glass of a person, if the distance of distinct vision is 75cm.
A. 75.2 cm
B. 25.6 cm
C. 100.4 cm
D. 37.5 cm
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Correct Answer - D
Given, `v=-75 cm`
`u=-25 cm`
We know that, lens formula, we have
`(1)/(f)=(1)/(v)-(1)/(u)`
`(1)/(f)=(-1)/(75)+(1)/(25)`
`(1)/(f)=(1)/(25)-(1)/(75)`
`(1)/(f)=(3-1)/(75)`
`(1)/(f)=(2)/(75)`
Focal length of a glass, `f=(75)/(2)=37.5 cm`
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