Regular Reflection:
The reflection in which parallel incident rays remain parallel after reflection and go only in one direction is called regular reflection.
§ In regular reflection, a parallel beam of incident light is reflected as a parallel beam in one direction.
§ Regular reflection of light occurs from smooth surfaces like that of a plane mirror (or highly polished metal surfaces).
§ Smooth surface produces a clear image of an object due to regular reflection of light.
§ A highly polished metal surface and a still water surface also produce regular reflection of light and form images. This is why we can see our face in a polished metal object as well as in the still water surface of a pond or lake.
Diffuse Reflection:
The reflection in which parallel incident rays do not remain parallel after reflection is called diffuse reflection.
§ In diffuse reflection, a parallel beam of incident light is reflected in different directions. they are scattered in different directions.
§ The diffuse reflection is also known as irregular reflection or scattering.
§ The diffuse reflection of light takes place from rough surfaces like that of paper, cardboard, chalk, table, chair, walls and unpolished metal objects.
§ A rough surface (like that of paper) does not produce an image of the object due to diffuse reflection of light.
The diffuse reflection of light from a rough surface can be explained as follows :
The particles of a rough surface (like that of paper) are all facing in different directions. Due to this, the angles of incidence for all the parallel rays of light falling on a rough surface are different and hence the angles of reflection for all the rays of light are also different. Since the angles of incidence and the angles of reflection are different, the parallel rays of light falling on a rough surface go in different directions.
The laws of reflection are valid at each point even on the rough surface of an object. The surfaces of most of the objects are rough (or uneven) to some extent. So, most of the objects around us cause diffuse reflection of light and scatter the light falling on them in all directions.
In fact, we can see these objects only because they scatter light rays falling on them in all directions. For example, a book lying on a table can be seen from all parts of the room due to diffuse reflection of light from its surface,
A cinema screen has a rough surface and causes diffuse reflection of light falling on it. The cinema screen receives light from a film projector and scatters it in all directions in the cinema hall so thát people sitting anywhere in the hall can see the picture focused on the screen.
Object :
Anything which gives out light rays (either its own or reflected by it) is called an object.
A bulb, a candle, a pin-head, an arrow, our face, or a tree, are all examples of objects
The objects can be of two types :
Luminous objects :
The objects which emit their own light are called luminous objects.
e.g The objects like the sun, other stars, electric bulb, tube-light, torch, candle and fire, etc., are luminous objects.
Non-luminous objects :
Those objects which do not emit light themselves but only reflect (or scatter) the light which falls on them, are called non-luminous objects .
e.g A flower, chair, table, book, trees, other plants, human beings, fan, bed, mirror, diamond, walls, floor, and road, etc., are all non-luminous objects.
Image :
An image is formed when the light rays coming from an object meet (or appear to meet) at a point, after reflection or refraction .
The images are of two types :
Real Images :
The image which can be obtained on a screen is called a real image.
e.g The images formed on a cinema screen .
When light rays coming from an object meet at a point after reflection or refraction then real image is formed.
Real image is always inverted.
Virtual image :
The image which cannot be obtained on a screen is called a virtual image.
· The image of our face in a plane mirror is an example of virtual image
· Virtual images are also called unreal images.
· When light rays coming from an object appear to spread from a point after reflection or refraction then virtual image is formed.
· A virtual image cannot be formed on a screen because light rays do not actually pass through a virtual image.
· Virtual image is always erect.
· A plane mirror always forms virtual images.
· A convex mirror also forms only virtual images.
Lateral Inversion :
When an object is placed in front of a plane mirror, then the right side of object appears to become the left side of image; and the left side of object appears to become the right side of image. This change of sides of an 'object and its 'mirror image' is called lateral inversion.
i.e The effect of reversing the sides of an object and its image is called lateral inversion.
The image formed in a plane mirror is laterally inverted. In other words, the image formed in a plane mirror is 'sideways reversed' with respect to the object.
Characteristics of an image formed by a plane mirror.
1. The image formed in a plane mirror is virtual. It cannot be received on screen.
2. The image formed in a plane mirror is erect. It is the same side up as the object.
3. The image in a plane mirror is of the same size as the object.
3. The image in a plane mirror is of the same size as the object.
4. The image formed by a plane mirror is at the same distance behind the mirror as the object is in front of the mirror.
5. 'The image formed in a plane mirror is laterally inverted (or sideways reversed).
Uses of Plane Mirrors
(i) Plane mirrors are used to see ourselves. The mirrors on our dressing table and in bathrooms are plane mirrors.
(ii) Plane mirrors are fixed on the inside walls of certain shops (like jewellery. shops) to make them look bigger.
(iii) Plane mirrors are fitted at blind turns of some busy roads so that drivers can see the vehicles coming from the other side and prevent accidents.
(iv) Plane mirrors are used in making periscopes.
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