Law of Reflection: We see many things around us. When you enter the darkroom you can see nothing but after lighting up the room it is possible to everything around us. The visibility is due to the reflection of light. The object reflects when light falls on it. The light which is reflected back is received by our eyes enabling us to see the objects. This phenomenon is due to the reflection of light which works upon the principle of the Laws of reflection. So in this article, we will study the Laws of reflection in detail.
Reflection of Light
Reflection of light is the bouncing back of the light. The angle at which it incident on the surface is called the angle of incident and the angle at which it reflects back is called the angle of reflection. At the point of incidence and reflected ray a line drawn perpendicular to the surface is normal.
Types of Reflection
There are two types of reflection, that is-
- Regular/Specular Reflection: In this type, reflection takes place on a smooth surface. The image formed by such reflection is smooth. and visible.
- Irregular/Diffused Reflection: In this type, reflection takes place on a diffused or irregular surface. Diffused light makes everything visible around us.
Terms in Relation to the Law of Reflection
Some of the terms related to the Law of Reflection-
Incident Ray- The ray of light which falls on the surface from the source of such a ray is called the incident ray.
Reflected Ray- The ray of light which is reflected back after hitting the surface is called the reflected ray.
The angle of Incidence – The angle formed between the incident ray and the point of incidence is called the angle of incidence.
The angle of Reflection – The angle formed between the reflected ray and the point of incidence is called the angle of reflection.
Normal – A straight line perpendicular to the reflecting surface which separated the plane of incidence and the plane of reflection is called normal.
Law of Reflection
There are basically two laws of reflection, these are-
- The first law, that is, the primary law says the angle formed between the incident ray and the normal is equal to the angle formed between the normal and reflected ray.
- The incident ray, the normal and the reflected ray, all lie on the same point of contact.
Law of Reflection Formula
The law of Reflection formula is the term that is used to state the relationship between the angle of incidence and the angle of reflection. It can be written as-
Angle of incidence = Angle of reflection
∠i = ∠r
The reflecting surface of a spherical mirror may be curved inwards or it may be outwards. A spherical mirror, whose reflecting surface is curved inwards is referred to as a concave mirror. A spherical mirror whose reflecting surface is curved outwards is referred to as a convex mirror.
Use of Concave Mirror:
- Useful in torches, searchlights, and headlights of vehicles so as to get powerful beams of light.
- The common use of concave mirrors is shaving mirrors.
- Dentists use such mirrors to see bigger images of the teeth of patients.
- They are used to focus sunlight to produce heat in solar furnaces.
Use of Convex Mirror:
- Used in shops and in supermarkets in order to detect bulgars.
- Useful in making lenses.
- Used in magnifying glasses and telescopes.
- Used to reflect street lights as they reflect over a wide area.
- Side-view mirrors.
Uses of Reflection of Light
Some of the uses of Reflection of light are-
- Periscopes(to view advancing enemies on the battlefield.)
- Medical treatment.
- Optical Communications.
- Useful in measuring the distance accurately.
- useful in hearing the echo of sound.
Solved Example of Law of Reflection
Example 1: What will be the incident angle if the angle between the mirror surface and the incident ray is 40°?
Solution: As we know,
∠i + Angle between mirrors surface and incident ray = 90°
∠i + 40° = 90°
∠i = 90°-40°
∠i = 50°
Therefore, the angle of the incident is 50°
Example 2: If the angle of incidence is 60° then what will be the angle of reflection?
Solution: As we know, ∠i = ∠r
Given that ∠i = 60°
∠r is 60°
Example 3: A ray of light that strikes the plane mirror at an angle of 30° with the surface.
(i) Calculate ∠i.
(ii) Calculate ∠r.
(iii) Calculate the angle made by the reflected ray and the plane surface
Solution: As we know,
(i) ∠i + Angle between mirrors surface and incident ray = 90°
∠i + 30° = 90°
∠i = 90° -30°
∠i = 60°
(ii) As we know, ∠i = ∠r
So, ∠r= 60°
(iii) Angle made by the reflected ray and the plane surface = 90° –∠r
= 90° –∠r
= 90° – 60°
The angle made by the reflected ray and the plane surface is 30°