Class 10 Science (physics) Light: Reflection and Refraction

 ~ Reflection of Light 

We know that in a single homogenous  medium,light travels in a straight line. When two different media meet, there is a very thin boundary layer separating the two media. This extremely thin layer is called the interface of the surface of separation between the two media (see figure point 4.4).

When A Ray of light falls on an interface of the two different media, any of the following three events may take place : 

i) A part of the incident light is

absorbed in the second medium.

ii) A part of the incident light is reflected

 back to the first medium and the

 phenomena is called reflection of light.

iii) a part of incident light is

transmitted through the second medium,

 with a change in the direction of

 propagation of light. This phenomenon

 is called refraction of light.

If most of incident light after interacting

 with a boundary separating the two

 media comes back in the medium full

 the phenomenon is called reflection of

 light.

Thus, 

The phenomenon of bouncing back of light in the same medium after striking the surface of any object is called reflection of light. 

The Reflection is of Two Types

1. Regular Reflection : if the reflecting

 surface is smooth and well polished, The

 parallel rays spelling on it are reflected

 parallel to each other coma that is the

 reflected light goes in one particular

 direction [see figure point 4.5 a)] 

this is regular reflection. The smooth and

 well polished surface is a mirror. Silver

metal is one of the best reflectors of light. So, ordinary Mirrors are made by depositing a thin layer of silver metal on one side of a plane glass sheet.

The Silver thus deposited is then

protected by a coat of red paint. stop the

 regular reflection of light in a mirror

 takes place at the surface where silver is

 coated. A plane mirror is represented by

 a straight line [see figure point 4.5(a)],

  having a large number of short of

 clients showing back of the mirror.

2. Irregular reflection or diffused reflection : when a

 parallel beam of light falls on the rough

surface, in the rays of light are scattered

(reflected) in all possible directions [see

figure 4.5 (b)]. such a reflection is called

 an irregular reflection or diffused

 reflection.  It is also known as scattering

of light. In fact, almost all the objects are

 seen by diffused reflection. For example, it

is due to diffuse reflection that the letters on

the this page are visible to us. Some of the

scattering light falls in our eyes, enabling us

to see the letters.

~ LAWS OF REFLECTION. 

When light suffers reflection from a well polished smooth surface, it obeys following two laws, as known as the laws of reflection.

First law : the incident ray, the reflected ray and the normal to the reflecting surface at the point of incident, all lie in the same plane.

Figure 4.6 shows that falling on plane mirror m m along a is a reflected along over.

Thus O is incident ray and OB is reflected ray. ON is normal to the mirror  at O. The point O of the mirror is called the point of incidence. 

Second law : angle of incidence, I is always equal to the angle of reflection, r, i.e.,  ∠i = ∠r.

Here, angle of incidence, i is the angle which the incident ray AO makes with the normal to the mirror and, angle of reflection, r is the angle which the reflected ray OB makes with the normal to the mirror.

In Fig.4.6, ∠AON = i and  ∠NOB = r 

    Thus, according to the second law, 

             ∠AON = ∠NOB, i.e.,.    ∠i = ∠r. 

     To Be Continued...