How does the eye control the amount of light entering it ?

Which of the following controls the amount of light entering into the human eye?

Answer briefly : (a) How do you perceive the colour of an object ? (b) Which part of our body helps us in maintaining the body balance ? (c) How does the eye regulate the amount of light that falls on the retina.

On which factor does the colour of the scattered white light depend ?

On which factor does the required amount of heat depend to increase temperature in substance ?

How does the chemical method work ?

What is the net amount of heat entering the system in a cyclic process equivalent to ?

On which does the scattering of light depend ?