reflection by plane,concave and aonvex mirrors

Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected. Mirrors exhibit specular reflection.

Concave Mirror

A concave mirror is a type of curved mirror and it is concave to the right of the object. The reflective material is pasted on the side opposite to the object to be placed. The curve of the mirror is mostly a segment of sphere and hence concave mirrors are also referred as Concave Spherical Mirror.

Concave Mirror Image

Back to Top

When an object is placed at infinity, the rays coming from it are parallel to each other. Let us consider two rays, one striking the mirror at its pole and the other passing through the center of curvature. The ray which is incident at the pole gets reflected according to the law of reflection and the second ray which passes through the center of curvature of the mirror retraces its path. These rays after reflection form an image at the focus. The image formed is real, inverted and diminished.

The image is

• At F
• Real
• Inverted
• Diminished

When the Object is Placed beyond C: The two rays which are considered to obtain the image are:

• A ray passing through the center of curvature

• A ray parallel to the principal axis. The ray passing through the center of curvature retraces its path and the ray which is parallel to the principal axis passes through the focus after reflection. These rays after reflection meet at a point between C and F. The image is inverted, real and diminished

The image is

• Between C and F
• Real
• Inverted
• Diminished

When the Object is Placed at the Center of Curvature: Here we consider the two rays, one parallel to the principal axis and the other passing through the focus. The ray of light which is parallel to the principal axis passes through the focus after reflection. The other ray passing through the focus after reflection emerges parallel to the axis. After reflection these rays meet at the center of curvature to form an inverted image, which is real and of the same size as the object. The image is

• At C
• Real
• Inverted
• Same size as object

When the Object is between C and F: Here we consider a ray of light which is parallel to the principal axis and another ray passing through the focus. The ray which is parallel to the principal axis passes through the principal focus and the ray which passes through the focus after reflection emerges parallel to the principal axis. The reflected rays meet at a point beyond C and the image is real, inverted and magnified. The image is

• Beyond C
• Real
• Inverted
• Magnified

When the Object is between C and F: Here, we consider a ray of light which is parallel to the principal axis and another ray passing through the center of curvature. The ray which is parallel to the principal axis passes through the focus and the ray which passes through the center of curvature retraces its path. The reflected rays are parallel to each other, and would meet only at infinity i.e., the image is formed at infinity and it is a real, inverted, enlarged image of the object.

The image is

• At infinity
• Real
• Inverted
• Magnified

When the Object is between the Pole and the Focus : Here we consider a ray of light which is parallel to the incident ray and another ray which is passing through the center of curvature. The ray which is passing through the center of curvature retraces its path and the other ray which is parallel to the principal axis after reflection passes through the focus. These rays appear to meet behind the mirror when the reflected rays are extended backwards. The image is virtual, erect and magnified.

The nature and size of Concave Mirror Image of an object placed in front of a concave mirror depends on the position of the object with respect to the mirror.

Convex Mirror

A convex mirror is a curved mirror which has a bulge towards the object. In other words, the coating of reflex material is done interior of the curved surface. Mostly the curved surface is a spherical segment. Convex mirrors are widely used in many practical applications due to its inherent reflection properties. Convex mirrors used as rear view mirrors, in staircase on the double-deck buses, vigilance mirrors in big shops and in showrooms.he intersection of these reflected rays decide the nature and location of the image. 

Let MM’ be a convex mirror and AB be an object placed at any point in front of the mirror. The ray AP from point A of the object, parallel to the principal axis hits the mirror at P and ‘appears’ to pass through the focus as ray PY’. But in effect it is reflected at P as ray PY. Another ray AO from the same point is reflected as ray OX but ‘appears’ to pass through as ray OX’ inside the mirror. The rays PY’ and OX’ intersect at A’ and forms a virtual image A’B’. When the object AB moves closer to the mirror, the line YY’ remains the same but the angle POA’ goes increasing. As a result, the size of the image A’B’ increases. But the maximum limit of the size of the image is approximately the size of the object when the object touches the mirror. On the other hand when the object AB moves away from the mirror, the image becomes smaller and smaller. Thus, the images in convex mirrors are reduced, upright, and always lie within the virtual focal length.   

The following rays coming from an object are usually used to construct the ray diagrams for locating the images formed by a convex mirror.

(i) The diagram shows a ray of light traveling parallel the principal axis after reflection from a convex mirror appears to come from its focus behind the mirror.

(ii) A ray of light traveling towards the centre of curvature behind the mirror hits the mirror at 90° and is reflected back its own path. This is shown in the diagram given below.