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

Answer

Given: Power of lens (P)= 1.5 D
To find: Focal length (f)= ?
Formula : `P=1/(f(m))`

Explanation

`P=1/(f(m))`
`therefore f= 1/p`
`therefore f= 1/(1.5)`
`therefore f= 10/15 `
`therefore f= 2/3 = 0.67 m`
Since of is + ve, lens used convex f=0.67 m The defect is Hypermetropia (farsightedness)