A person uses lenses of $+2.0 \text{ D}$ power in his spectacles for the correction of his vision. (a) Name the defect of vision the person is suffering from. (b) List two causes of this defect. (c) Determine the focal length of the lenses used in the spectacles.

The person is using lenses of $+2.0 \text{ D}$ power in his spectacles, which means the lenses are convex lenses. Convex lenses are used to correct hypermetropia (far-sightedness). The two causes of hypermetropia are: (i) insufficient curvature of the eye lens, or (ii) shortening of the eyeball. The focal length of the lenses used in the spectacles can be calculated using the formula: $f = \frac{1}{P}$ where $P$ is the power of the lens.