Reflection in Plane Mirrors

Light is a form of energy.  Light makes things around us visible. Objects that give out light on their own are called luminous objects. Objects that do not give out light on their own are called non-luminous objects. They just reflect light that falls on them. When light reflected from an object enters into our eyes, the object becomes visible to us. A mirror changes the direction of light that falls on it. The light ray that falls on a mirror is called the incident light ray. The ray that comes back from the surface after reflection is called the reflected light ray.

The point where the incident ray strikes the reflecting surface is called the point of incidence.  A line drawn perpendicular to the mirror at the point of incidence is the normal. According to the laws of reflection, the incident ray, the normal at the point of incidence, and the reflected ray lie in the same plane; and the angle of incidence is equal to the angle of reflection.

Characteristics of Image Formed in a Plane Mirror

The image formed by a plane mirror is:

       •  of the same size as that of the object
       •  left-right inverted
       •  erect and virtual
       •  formed behind the mirror at the same distance as the distance of the object in front of the mirror

If a set of parallel rays, after reflection from a surface, are parallel, then the reflection is termed as regular reflection. The reflection from a plane mirror is an example of regular reflection. If the incident rays are parallel, but the reflected rays are not parallel, then it is called diffused reflection or irregular reflection. The reflection from an uneven surface is diffused reflection. If a reflected light ray is reflected again on being incident on another surface, it is termed multiple reflections.

Multiple reflections are used in periscopes. Periscopes are used in submarines, war tanks and by soldiers in bunkers to see objects that are not visible directly. In a barber’s shop, we see the back of the head using multiple reflections of two mirrors. In a kaleidoscope, beautiful patterns are formed due to multiple reflections.

Summary

Light is a form of energy.  Light makes things around us visible. Objects that give out light on their own are called luminous objects. Objects that do not give out light on their own are called non-luminous objects. They just reflect light that falls on them. When light reflected from an object enters into our eyes, the object becomes visible to us. A mirror changes the direction of light that falls on it. The light ray that falls on a mirror is called the incident light ray. The ray that comes back from the surface after reflection is called the reflected light ray.

The point where the incident ray strikes the reflecting surface is called the point of incidence.  A line drawn perpendicular to the mirror at the point of incidence is the normal. According to the laws of reflection, the incident ray, the normal at the point of incidence, and the reflected ray lie in the same plane; and the angle of incidence is equal to the angle of reflection.

Characteristics of Image Formed in a Plane Mirror

The image formed by a plane mirror is:

       •  of the same size as that of the object
       •  left-right inverted
       •  erect and virtual
       •  formed behind the mirror at the same distance as the distance of the object in front of the mirror

If a set of parallel rays, after reflection from a surface, are parallel, then the reflection is termed as regular reflection. The reflection from a plane mirror is an example of regular reflection. If the incident rays are parallel, but the reflected rays are not parallel, then it is called diffused reflection or irregular reflection. The reflection from an uneven surface is diffused reflection. If a reflected light ray is reflected again on being incident on another surface, it is termed multiple reflections.

Multiple reflections are used in periscopes. Periscopes are used in submarines, war tanks and by soldiers in bunkers to see objects that are not visible directly. In a barber’s shop, we see the back of the head using multiple reflections of two mirrors. In a kaleidoscope, beautiful patterns are formed due to multiple reflections.

Videos

Activities


Activity 1

Sciencekids has deveoped an interactive online activity in which one can choose and drag a plane mirror in the path of light to illuminate various objects. By changing the position of the mirror the angle of incidence and hence the angle of reflection can be changed. Two mirrors can be used simultaneously too.

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Activity 2

Pearson.com.au has created an interative simulation in which one can change the position of the light source or the angle of the mirror to see how the angle of reflection changes. This simulation gives a virtual experimental set up to verify the law of reflection for different angles of incidence. One can see that the law is valid for all colours of light. Also there is a fun game to test the understanding of reflection of light.

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References

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