Reflection of light is the phenomenon in which light rays bounce back into the same medium after striking a smooth, polished surface, such as a mirror. When light strikes a reflecting surface, it changes direction and is reflected rather than passing through the surface.
During reflection, the angle of incidence is equal to the angle of reflection, and the incident ray, the reflected ray, and the normal at the point of incidence all lie in the same plane. This phenomenon helps us to see objects and images in mirrors.
- Normal: A perpendicular drawn to the reflecting surface at point M (known as the point of incidence) is called the normal to the reflecting surface.
- Incident Ray: A ray of light that falls on the reflecting surface from a light source or an object is called the incident ray.
- Reflected Ray: A ray of light that arises from the reflecting surface after reflection from it is called a reflected ray.
- Angle of Incidence: The angle between the incident ray and the normal to the point of incidence on the reflecting surface is known as the incident angle or angle of incidence. It is denoted by ∠i.
- Angle of Reflection: The angle between the reflected ray and the normal to the point of incidence on the reflecting surface is known as the angle of reflection. It is denoted by ∠r.
- Principal axis: It is defined as a line that divides the two mediums, or the reflecting surface is called the principal axis.
Laws of Reflection
After understanding the meaning of reflection of light, it is important to learn the two fundamental laws of reflection. These laws help us determine how a light ray reflects when it strikes different surfaces, such as a plane mirror, water surface, or polished metal.
- First Law: The incident ray, the reflected ray, and the normal at the point of incidence all lie in the same plane.
- Second Law: The angle of incidence (∠i) is always equal to the angle of reflection (∠r).
Types
Regular (Specular) Reflection
A bright and clear reflection like the one seen in a mirror is called "specular" (regular) reflection. It occurs when light falls on a smooth and polished surface. Mirrors are made by coating glass with a thin layer of highly reflective material, which reflects most of the light that falls on it. Since the surface is very smooth, the angles of reflection at different points remain almost the same. As a result, the reflected rays stay parallel and produce a sharp image without haze or blurring.
Diffused Reflection
It reflection occurs when light falls on a rough or uneven surface. Most surfaces around us are not perfectly smooth and may contain dust, scratches, dents, or other irregularities. Because of this roughness, the reflected light does not travel in a single direction.
When light rays strike such uneven surfaces, they are reflected in many different directions. Although the laws of reflection are still followed at each point, the angles of reflection vary from place to place. As a result, no clear image is formed, but this type of reflection helps us see ordinary, non-shiny objects around us.
Reflection of light from the Plane Mirror
When light rays strike a plane (flat) mirror, they are reflected back according to the laws of reflection, where the angle of incidence is equal to the angle of reflection. The incident ray, the reflected ray, and the normal all lie in the same plane.
The image formed by a plane mirror appears behind the mirror. This image is virtual, erect, and of the same size as the object. Because the rays only appear to come from behind the mirror, the image cannot be obtained on a screen.
Regular vs Irregular Reflection
Regular Reflection | Irregular Reflection |
|---|---|
| Occurs on smooth and polished surfaces such as plane mirrors. | Occurs on rough and uneven surfaces such as wood, paper, or walls. |
The reflected rays remain parallel to each other after reflection. | The reflected rays scatter in different directions after reflection. |
A clear and sharp image is formed. | No clear image is formed; the image appears blurred or distorted. |
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Solved Problems
Question 1: A light ray strikes a plane mirror with an angle of incidence of 35°. Find the angle between the incident ray and the reflected ray.
Solution: Angle between incident ray and reflected ray = 2 × angle of incidence
= 2 × 35°
= 70°
Question 2: Question: A light ray makes an angle of 25° with the mirror surface. Find the angle of reflection.
Solution: Angle of incidence = 90° − angle with mirror surface
= 90° − 25°
= 65°
Angle of reflection = Angle of incidence = 65°
Question 3: The angle between the incident ray and the normal is 50°. Find the angle of reflection.
Solution: Angle between incident ray and normal = Angle of incidence
∠i = 50°
According to the law of reflection
∠r = ∠i = 50°
Question 4: The angle between the incident ray and reflected ray is 120°. Find the angle of incidence.
Solution: Angle between incident ray and reflected ray = 2 × angle of incidence
2i = 120°
i = 120° / 2
i = 60°
Unsolved Problems
Question 1: A ray of light strikes a plane mirror with an angle of incidence of 37°. Find the angle between the incident ray and the reflected ray.
Question 2: A light ray makes an angle of 52° with the normal to a plane mirror. Find the angle of reflection.
Question 3: A ray of light makes an angle of 18° with the mirror surface. Determine the angle of incidence.
Question 4: The angle between the incident ray and the reflected ray is 140°. Find the angle of incidence.
Question 5: A light ray strikes a plane mirror, and the angle of reflection is 63°. Find the angle made by the incident ray with the mirror surface.