(i) Explain the sign conventions of lenses.
(ii) Define dispersion of light.

Explanation

(i) (a) The object is always placed on the left side of the lens.
(b) All the distances are measured from the optical centre of the lens.
(c) The distances measured in the same direction as that of incident light are taken as positive.
(d) The distances measured against the direction of incident light are taken as negative.
(e) The distances measured upward and perpendicular to the principal axis is taken as positive.
(f). The distances measured downward and perpendicular to the principal axis is taken as negative.
(ii) When a beam of white light or composite light is refracted through any transparent media such as glass or water, it is split into its component colours. This phenomenon is called as dispersion of light.