Reflection of Light - Class 6 Notes & Olympiad Questions

Reflection of Light

a) When light travels and encounters a surface, it can bounce back. This bouncing back of the light is called reflection.
b) When light falls on an object, such as a mirror, a shiny metal surface, or even a piece of paper, some of the light is sent back or reflected. This bouncing back of light allows us to see objects and their images.
c) When light reflects off a smooth surface, like a mirror, it creates a clear and sharp image. So, if you stand in front of a mirror, the light from you reflects off the mirror and enters your eyes, allowing you to see your own reflection.
d) Reflection is not just about mirrors; it happens with other surfaces too. For example, if you shine a flashlight on a smooth table, the light will bounce off the table and illuminate the area around it.
e) Reflection of light is essential for our ability to see objects. When light reflects off an object and reaches our eyes, it creates an image in our brain, allowing us to perceive the object. That's why we can see ourselves in mirrors or admire the world around us.

Incident Ray and Reflected Ray

Incident Ray

a) An incident ray is a light ray that approaches and hits a surface.
b) It's the path along which light travels before reaching the surface.
c) For example, imagine a beam of light coming from a flashlight and hitting a mirror. The beam of light travelling from the flashlight to the mirror is the incident ray.

Reflected Ray

a) After the incident ray hits the surface, it undergoes reflection, which means it bounces off the surface.
b) The reflected ray is the light ray that bounces off the surface after reflection. It's the path along which light travels after being reflected.
c) In the case of the mirror, the beam of light that bounces off the mirror and travels away from it is the reflected ray.

Types of Reflection

There are two main types of reflection: regular reflection and diffused reflection.

Regular reflection

a) Regular reflection occurs when light hits a smooth and even surface, like a mirror or calm water.
b) In this case, the light rays bounce off the surface in a very organised manner, forming a clear image. This is why you can see a crisp and accurate reflection in a mirror.

Diffused reflection

a) Diffused reflection happens when light falls on an irregular or rough surface, such as a piece of paper or a textured wall.
b) The surface scatters the light in different directions, causing it to bounce off randomly.
c) As a result, the reflected light does not create a clear image but rather spreads out and illuminates the surroundings.
d) This is why you can't see a distinct reflection on a rough or non-reflective surface like paper.

Laws of Reflection

When light hits a smooth and shiny surface, like a mirror, it follows two important rules called the laws of reflection:

First Law of Reflection

a) The first law of reflection states that the angle at which light hits a surface is the same as the angle at which it bounces off.
b) Imagine you throw a ball towards a wall, and it bounces back at the same angle you threw it. Similarly, light does the same thing when it hits a mirror or a smooth surface.

Second Law of Reflection

a) The second law of reflection says that the reflected light always bounces off the surface in a way that the incoming light ray, the reflected light ray, and a line perpendicular to the surface called the normal, all lie in the same plane.
b) Basically, this means that the light reflects back in a predictable way, following a specific pattern.

Plane Mirror

a) A plane mirror is a flat mirror with a smooth and shiny surface.
b) When light falls on a plane mirror, it undergoes regular reflection, meaning that the light rays bounce off the mirror in an organised manner.

Characteristics of the Image formed by a Plane Mirror

1. Virtual and Erect Image

a) The image formed by a plane mirror is virtual, which means it cannot be projected onto a screen. It appears to be there, but it cannot be captured.
b) It appears to be behind the mirror, but it is not a real object.
c) The image is also erect, which means it appears in the same orientation as the object.
d) If the object is upright, the erect image will also be upright. If the object is inverted, the erect image will also be inverted.

2. Same Size as the Object

a) The size of the image formed by a plane mirror is the same as that of the object.
b) If you stand in front of a plane mirror, the reflected image will have the exact height and width as you do.

3. Image Distance

a) The image formed by a plane mirror appears to be the same distance behind the mirror as the object is in front of it.
b) So, if you stand 1 meter away from the mirror, your image will also appear to be 1 meter behind the mirror.

4. Lateral Inversion

a) The image formed by a plane mirror is laterally inverted.
b) This means that the right side of the object appears as the left side of the image, and vice versa.
c) For example, if you have a paper with the word "OPEN" written on it and you place it in front of a plane mirror, the reflected image will be:

Difference between an Image and a Shadow

An image and a shadow are both created when light interacts with objects, but they have some distinct differences: