1. NATURE OF LIGHT:
Light:
The physical cause, with the help of which our eyes experience the
sensation of vision, is known as light.
(or) the form of energy, which excites our retina and produce the sensation
of vision, is known as light.
Ray of light: The path of light energy from one
point to another is known as a ray of light.
properties of
light: i) No
material medium is required for the propagation
of light energy i.e. it travels even in vacuum.
ii) Its velocity is constant in all inertial frames. It is independent of the relative velocity
between source and the observer.
iii) velocity of light is maximum in vacuum whose value
is 3 x 
m/s.
m/s.
iv) Light can emit electrons from the metal surface i.e. it can produce
photoelectric effect.
v) Light propagates in straight lines.
vi) Light produce thermal effect and exerts pressure when incident upon
a surface. It proves that the light has
momentum and energy.
vii) Light exhibits the phenomena of reflection, refraction,
interference, diffraction, polarisation, and double refraction.
viii) The properties of the medium through which light passes remain
unchanged.
ix) The velocity of light is different in different media. In rarer medium, it is more and in denser
medium, the velocity of light is less.
