Question

Determine the focal length of the lenses used in the spectacles.

Hint:

For correcting hypermetropia, convex lenses are used, and their power is calculated as \( P = \frac{1}{f} \). A positive power indicates the use of convex lenses.

Answer 1

A lens's power \( P \) and focal length \( f \) are related by: \[ P = \frac{1}{f} \] where \( P \) is in diopters (D) and \( f \) is in meters.
If the power \( P = +2.0 \, {D} \), the focal length is: \[ f = \frac{1}{P} = \frac{1}{2.0} = 0.5 \, {m} \] 
Therefore, the spectacles' lenses have a focal length of 0.5 meters.