$A$ person suffering from an eye defect uses lenses of power $-1 \,D$. Identify the eye defect. Draw a suitable diagram to illustrate how this type of lens corrects the defect. Give the nature of the corrective lens to be used. Also,calculate the focal length of the corrective lens.

(N/A) The person is suffering from myopia (short-sightedness).
$A$ concave lens is used to correct this defect.
The nature of the corrective lens is a concave lens (diverging lens).
We know that the power of a lens $P = 1 / f$ (where $f$ is in meters).
Given $P = -1 \,D$.
Therefore,$f = 1 / P = 1 / (-1) = -1 \,m = -100 \,cm$.
The negative sign indicates that the lens is concave.