Mirrors and Reflections

Mirror

We all have seen the plane mirror. It is very commonly used in our life. We used that in the car, dressing room etc. Plane mirror are formed by layering molten aluminum or silver onto the back of a sheet of glass inside a vacuum

Reflection of Light

We see our face in the Mirror. This is possible through the phenomenon Reflection of light. Basically Light rays reflected from parts of our body fall on mirror and are reflected back. When these reflected rays reach our eyes (reflected on our retina), we can see the image in the mirror.
So reflection of light is changing the direction of the light.
Image formation by Plane Mirror

  • A plane mirror reflects the light that falls on it.
  • The beam of light that falls on the mirror is called incident ray, while the light that reflects called the reflected ray.
  • The angle of incident ray equals to the angle of the reflected ray.
  • The incident ray, reflected ray and normal ray lies at the common point of the mirror (Figure 11).
  • A plane mirror has a property of lateral inversion in which the image formed in the mirror has an opposite side. For example, when you see your image in the mirror your right hand becomes left and your left hand becomes right.
  • The image formed is erect, same size and laterally inverted. It retains the same colour as the object.

All of us are used to seeing a mirror every day. The image that we see in a mirror is called Reflection. The mirror deflects the direction of the light that falls upon it.

Fig: A Mirror Changing the direction of light as it falls on it

Reflection Surfaces
We say light is reflected when it bounces off a surface. Reflection of light helps us to see most of the things around us.
Reflection of light by a surface depends on the nature of the surface. A rough and bumpy surface (also called an irregular surface) reflects a parallel beam of light incident upon it in different directions (Fig. 13.5). A good example of a rough surface is bark of a tree and blanket. This kind of reflection is called diffused reflection.

A smooth surface (a highly polished surface) reflects a parallel beam of light incident upon it in one direction. (Fig. 13.6). A good example of a smooth surface is a mirror. When you stand in

front of a mirror, you can see yourself in the mirror. This is called your image.

A very interesting phenomenon occurs when an object forms an image by reflection. This is something all of us must have noticed while seeing ourselves in the mirror. When we lift our right hand, the image in the mirror appears to lift its left hand. This seeming left-right reversal is called Lateral inversion.

Lateral inversion: Right side of the object appears as left side in the image formed by a plane mirror. For example, if we show our right hand, image in the mirror will show as left hand.

In a mirror, if you see another person, surely the other person can also see you in that mirror.
An image is different from a shadow. Some of the differences between an image and a shadow are given in Table 13.1

SUMMARY

Source of light: An object that gives out light (luminous object) is called a source of light.

Transparent material: A material that transmits all the light is called a transparent material.

Translucent material: A material that transmits some amount of light is called a translucent material.

Opaque material: A material that completely blocks the light is called an opaque material.

Shadow: An area of darkness formed by an opaque object obstructing light is called a shadow.