10. LIGHT – REFLECTION AND REFRACTION
Optics is the study of behaviour and properties of light.
An object reflects light
that falls on it. Eyes receive the reflected light and thus we see that object.
We see through a transparent
medium as light is transmitted through it.
Light seems to travel in
straight lines. A small source of light casts a sharp shadow of an
opaque object. It is usually indicated as a ray of light.
If there is very small opaque object on the path of light, it shows a tendency to bend around it. This effect is called diffraction. Here, the straight-line concept fails.
Such phenomena can be explained by considering light as a wave. But Wave theory often becomes inadequate for treatment of the interaction of light with matter, and light often behaves like a stream of particles.
Quantum theory says that light is neither a ‘wave’ nor a ‘particle’. It reconciles the particle properties with the wave nature.
REFLECTION
OF LIGHT
Laws of
reflection of light:
(i) Angle of incidence is equal to angle of reflection.
(ii) The incident ray, the
normal to the mirror at the point of incidence and reflected ray, all lie in same
plane.
These laws are applicable
to all types of reflecting surfaces including spherical surfaces.
A highly polished
surface, such as a mirror, reflects most of the light falling on it.
Image formed by a plane
mirror is virtual and erect. The size of the image is equal
to that of the object. The image formed is as far behind the mirror as the
object is in front of it. Further, the image is laterally inverted.
Image
formation by curved mirror:
Consider the curved
surface of a large shining spoon is a curved mirror. The image at its concave
side is real, inverted and diminished. If the spoon is moved
away, image becomes smaller.
Image at the convex
side is virtual, erect & diminished. If the spoon is moved
away, image becomes smaller.
The most commonly used type of curved mirror is the spherical mirror.
