$A$ 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.

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(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.

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