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Doctor has presecribed a lens having pow...

Doctor has presecribed a lens having power + 1.5D. What will be the focal length of the lens ? What is the type of the lens and what must be the defect of vision ?

Text Solution

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The correct Answer is:
The prescribed lens is convex lens of focal length +0.67 m and the defect in vision is hypermetropia (farsightedness).
Given: Power (P) =+1.5 D
To find: Focal length (f)
Formula: `P=(1)/(f(m))`
Calculation: From formula,
`f=(1.5)=+0.67 m`
The prescribed lens is convex lens as the focal length is positive. Convex lens has positive focal length and it is used for the correction of farsightedness or hypermetropia. Thus, the defect in vision is hypermetropia (farsightedness).
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