Page 37 - Physics 10_Float

GEOMETRICAL OPTICS

Light is the main focus of this unit. We shall describe different Physics of Light
phenomena of light such as reflection, refraction and total
internal reflection. We will learn how images are formed by
mirrors and lenses and will discuss working principle of
compound microscope and telescope.

12.1 REFLECTION OF LIGHT

Reflection of light is illustrated in Fig. 12.1. When a ray of light
We see a page of a book
from air along the path AO falls on a plane mirror M, it is
because light reflects from
reflected along the path OB. The ray AO is called incident ray
each part of the page in all
while the ray OB is called reflected ray. The angle between directions, so that some of the
incident ray AO and normal N, i.e., AON is called the angle < light rays from each part of the

of incidence represented by i. The angle between the normal page enter our eye. Because
almost no light is reflected by
and the reflected ray OB, i.e., < NOB is called angle of

the printed words, we “see”
reflection represented by r. them as black areas.
Normal
Incident ray Reflected ray
N
A B
Angle of Angle of For your information
incidence reflection In the early 1700s, there were
two ideas about the nature of
i r light: particle nature and wave
Plane mirror 90 o M
O nature. Newton put forward
Point of incidence the idea of corpuscular nature
of light. According to him, light
Fig. 12.1: Reflection of light consists of tiny, fast-moving
particles. Maxwell formulated
Now we can define the phenomenon of reflection as:
the wave theory of light. In
When light travelling in a certain medium falls on the 1802, Thomas Young proved
surface of another medium, a part of it turns back in the the wave nature of light
experimentally. In 1900,
same medium. Planck suggested that light
consists of small packets of
Laws of Reflection energy called photon. Later on
(i) The incident ray, the normal, and the reflected ray at the idea of photon was confirmed
by experiments. Now we know
point of incidence all lie in the same plane.
that light has dual nature; light
(ii) The angle of incidence is equal to the angle of reflection as well as particle nature.
i.e., i = r.

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