(a) List two causes of hypermetropia.(b) Draw ray diagrams showing (i) a hypermetropic eye and (ii) its correction using suitable optical device.

(a) The two causes of hypermetropia (or, long-sightedness) are as follows:

1. The low converging power of the eye lens (because of its large focal length), which causes the formation of the images of objects behind the retina, or

2. The eye ball is too short, which causes light to focus beyond the retina, instead of directly on the retina. 

(i) The ray diagram showing a hypermetropic eye.

(ii) The ray diagram showing its correction using a suitable optical device.

Explanation

 Hypermetropia, also known as long-sightedness or far-sightedness, is a defect of vision in which a person can't see the nearby object clearly (appears blurred), though can see the distant objects clearly. The near point of a hypermetropic eye is more than 25 cm away.

This defect occurs either due to the low converging power of the eye lens, (because of its large focal length). Or, due to the eye-ball being too short, which causes light to focus beyond the retina, instead of directly on the retina. 

It is corrected by using spectacles containing convex lenses, which should be of such a focal length (or power) that it forms a virtual image of the object (lying at the normal near point N of 25 cm) at the near point 'N' of the hypermetropic eye.