A person with a myopic eye can only see objects clearly up to a distance of $2\mathit{ m}$. What will be the power of the corrective lens required?

Given,
Far point or the focal length $f= -2\mathit{ m}$.
Since the corrective lens used is concave, the focal length considered is negative.
It is known that the power of a lens is the reciprocal of the focal length of the lens. Mathematically, 
$P=\frac{1}{f}$
Where $f$ is the focal length of the lens in metres.
On substituting the values, we get the power as:
$\Rightarrow P=\frac{1}{-2}$
$\Rightarrow P= -0.5\mathit{ D}$
Hence, the power of the lens required is $–0.5\mathit{ D}$.