Class 8, Science, Chapter-13, Lecture-1, Reflection (Notes)

LIGHT: 

Light is the form of energy consisting of electromagnetic waves that enables us to see objects from which it comes or from which it is reflected.

• Speed of Light in vacuum = 3 x 10⁸ ms ^–1
• Speed of Light depends on the medium of propagation

LUMINOUS OBJECTS:

The objects which emit their own light are called Luminous objects

• Examples: The Sun, Fire, Flame, Glowing Bulb etc

NON-LUMINOUS OBJECTS:

The objects which do not emit their own light are called Non Luminous objects

• Examples: Planets, Mirror, Table, Book etc
• Non-Luminous objects are also called ILLUMINATED objects.
• Non-Luminous objects become visible in the presence of light by reflecting the light to our eyes.

REFLECTION of Light:

The bouncing back of light rays which fall on the surface of a non-luminous object is termed as the Reflection of Light.

INCIDENT RAY:

The ray of light which falls on the surface of the mirror is termed as the Incident Ray.

POINT OF INCIDENCE:

The point on the surface of the mirror at which the incident ray strikes it is termed as the Point of Incidence.

REFLECTED RAY:

The ray of light which is sent back by the mirror is termed as the Reflected Ray.

NORMAL:

An imaginary line perpendicular to the surface of the mirror at the point of incidence is called the Normal at the point of incidence.

ANGLE OF INCIDENCE:

The angle between the incident ray and the normal at the point of incidence is termed as the Angle of Incidence.

• It is represented by $\angle i$.

ANGLE OF REFLECTION:

The angle between the reflected ray and the normal at the point of incidence is termed as the Angle of Reflection.

• It is represented by $\angle r$.

LAWS OF REFLECTIONS:

1. The angle of incidence ( i ) is always equal to the angle of reflection ( r ). 
   i.e. ${\angle i = \angle r}$
2. The incident ray, the reflected ray, and the normal to the mirror at the point of incidence all lie in the same plane.

REGULAR REFLECTION:

The reflection of light by a smooth surface in which a parallel beam of incident light is reflected as a parallel beam in one direction is termed as Regular Reflection.

IRREGULAR REFLECTION:

The reflection of light by a rough surface in which a parallel beam of incident light is reflected in different directions is termed as Irregular Reflection or Diffuse Reflection.

Differences Between