Reflection of Light
Light travels in a straight line. It can either be reflected or refracted.
Reflection of Light
The process through which light rays falling on the surface on an object are sent back is called reflection of light. Thus, when light falls on the surface of an object it sends back the light.
The objects having shiny or polished surface reflects more light compared to the objects having dull or unpolished surface. Silver metal is the best reflector of light. This is why plane mirror is made by depositing a thin layer of silver metal on one side of a plane glass sheet. The silver coating is protected by a red paint.
The straight line along which the light travels is called ray of light.
Regular Reflection and Diffuse Reflection of Light
In regular reflection, a parallel beam of incident light is reflected as a parallel beam in one direction. In this case , parallel incident rays remain parallel even after reflection and go only in one direction and it occurs from smooth surfaces like that of a plane mirror or highly polished metal surfaces. Thus, a plane mirror produces regular reflection of light. Since the angle of incidence and the angle of reflection are the same or equal, a beam of parallel rays falling on a smooth surface is reflected as a beam of parallel light rays in one direction only. It is explained below in the figure.
In diffuse reflection, a parallel beam of incident light is reflected in different directions. In this case, the parallel incident rays do not remain parallel after reflection, they are scattered in different directions. It is also known as irregular reflection or scattering and so, takes place from rough surfaces like that of paper, cardboard, chalk, table, chair, walls and unpolished metal objects. Since, the angle of incidence and angle of reflection are different, the parallel rays of light falling on a rough surface go in different directions as explained below in the figure.
Reflection of light from plane mirror
Before understanding the laws of reflection of light, lets understand the meaning of some important terms such as, incident ray, reflected ray, point of incidence, normal (at the point of incidence), angle of incidence and angle of reflection.
Incident ray: The ray of light falling on the surface of a mirror is called incident ray.
Point of incidence: The point at which the incident ray falls on the mirror surface is called point of incidence.
Reflected ray: The ray of light which is sent back by the mirror from the point of incidence is called reflected ray.
Normal: A line perpendicular or at the right angle to the mirror surface at the point of incidence is called normal.
Angle of incidence: The angle made by the incident ray with the normal is called angle of incidence.
Angle of reflection: The angle made by the reflected ray with the normal at point of incidence is called angle of reflection.
Laws of reflection of light
The laws of reflection of light apply to both plane mirror as well as spherical mirror. In this article we will discuss about the images formed by the plane mirror.
First law of reflection: According to the first law, the incident ray, reflected ray and normal, all lie in the same plane.
Second law of reflection: According to the second law, the angle of reflection is always equal to the angle of incidence.
Also, it is important to note that when a ray of light falls normally on the surface of the mirror then the angle of incidence and the angle of reflection for such a ray of light will be zero. This ray of light will be reflected back along the same path.
Objects and images
Anything which gives out light with off its own of reflected by it is called an object. For example, a bulb, a candle, a tree etc.
When the light rays coming from an object are reflected from a mirror then an optical appearance which is produced is called an image. For example, when we look into the mirror, we see the image of our face. Images are of two types, real image and virtual image.
Real image: The image which can be seen on screen is called real image.
Virtual image: The image which cannot be obtained on a screen is called virtual image.
When we stand in front of a mirror and lift our right hand than the image formed will lift its left hand. Therefore the right side of our body becomes the left side in its image and the left side of our body becomes the right side in its image in mirror.
The change of sides of an object in its mirror image is called lateral inversion. It happens due to reflection of light.
Formation of image in a plane mirror
The nature of image formed by a plane mirror is:
- Virtual and erect.
- Size of image formed is equal to the size of object.
- Image is formed behind the mirror.
- Image is at same distance behind the mirror as the object is in front of the mirror.
- Image formed in plane mirror is laterally inverted.
Uses of plane mirror
- Mirrors on our dressing table and bathrooms are plane mirrors and are used to see ourselves.
- They are fixed on the inside walls of jewellery shops to make them look big.
- They are fitted at blind turns on the roads so that the driver can see the vehicles coming from other side.
- Used in making periscopes.
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