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

The power of a lens \( P \) is related to its focal length \( f \) by the formula: \[ P = \frac{1}{f} \] where \( P \) is the power in diopters (D) and \( f \) is the focal length in meters. 
Given that the power \( P = +2.0 \, {D} \), we can calculate the focal length: \[ f = \frac{1}{P} = \frac{1}{2.0} = 0.5 \, {m} \] 
Thus, the focal length of the lenses used in the spectacles is 0.5 meters.