(i) Convex lenses are used as camera lenses.
(ii) Convex lenses are used as magnifying lenses.
(iii) Convex lenses are used in making microscope, telescope and slide projectors.
(iv) Convex lenses are used to correct the defect of vision called hypermetropia.

(i) Convex or bi-convex lens : It is a lens bounded by two spherical surfaces such that it is thicker at the centre than at the edges. It is a converging lens. So, a beam of light passing through it is converged to a point. So, a convex lens is also called as converging lens.
(ii) Concave or bi-concave Lens : It is a lens bounded by two spherical surfaces such that it is thinner at the centre than at the edges. It is a diverging lens. So, a parallel beam of light passing through it is diverged or spread out. So, a concave lens is also called as diverging lens.

(i) Mie scattering takes place when the diameter of the scatterer is similar to or larger than the wavelength of the incident light. It is also an elastic scattering. The amount of scattering is independent of wave length.
(ii) Mie scattering is caused by pollen, dust, smoke, water droplets, and other particles in the lower portion of the atmosphere.

Based on initial and final energy of the light beam, scattering can be classified as, (i) Elastic scattering, (ii) Inelastic scattering.
(i) Elastic scattering : If the energy of the incident beam of light and the scattered beam of light are same, then it is called as 'elastic scattering'
(ii) Inelastic scattering : If the energy of the incident beam of light and the scattered beam of light are not same, then it is called as 'inelastic scattering:

(i) Tiny water droplets are formed in the atmosphere due to rainfall. The rainbow is formed when sun light falling on these tiny water droplets undergoes dispersion.
(ii) When the sun light is incident on them, it is first refracted and dispersed at the front surface. When the refracted light falls on the back surface of the water droplet, it undergoes total internal reflection.
(iii) This reflected beam of coloured lights are refracted at the front surface of the water droplet. Thus, the rainbows can always be seen opposite to the sun.