A doctor has prescribed a corrective lens of power +1.5 D. What is the focal length and nature of the lens?
Question
A doctor has prescribed a corrective lens of power +1.5 D. What is the focal length and nature of the lens?
Solution
The power of a lens is given by the formula P = 1/f, where P is the power of the lens and f is the focal length of the lens. The power of the lens is given in diopters (D) and the focal length is given in meters (m).
Given that the power of the lens is +1.5 D, we can substitute this into the formula to find the focal length:
1.5 = 1/f
Rearranging the formula to solve for f gives:
f = 1/1.5
Therefore, the focal length of the lens is approximately 0.67 meters.
The positive sign of the power indicates that the lens is a converging or convex lens. This type of lens is used to correct hypermetropia or long-sightedness.
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