What is long-sightedness (hypermetropia)? List two causes for development of long-sightedness. Describe with a ray diagram, how this effect may be corrected by using spectacles?

State two main causes of a person developing near-sightedness. With the help of a ray-diagram, suggest how he can be helped to overcome this disability.

$\left(a\right)$ Explain the following terms used in relation to defects in vision and correction produced for them $\left(i\right)$ myopia $\left(ii\right)$ bifocal lenses $\left(iii\right)$ far-sightedness.

What will be the observed colour of the sky on a planet where there is no atmosphere? Why?