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Class 10, Science, Chapter-9, Lecture-1, Plane Mirror (Notes)

LIGHT:

Light is a form of energy consisting of electromagnetic waves that enables us to see objects from which it comes or from which it is reflected.

Speed of light in vacuum = 3 x 108 ms­—1

IMAGE:

A point where a number of light rays coming from a point source actually meet or appear to meet after reflection or refraction is termed as the image of the point source.

REAL IMAGE:

A point where a number of light rays coming from a point source actually meet after reflection or refraction is termed as a real image of the point source.

VIRTUAL IMAGE:

A point where a number of light rays coming from a point source do not actually meet but appear to meet after reflection or refraction is termed as a virtual image of the point source.

DIFFERENCES BETWEEN:

REAL IMAGE

VIRTUAL IMAGE

1. A real image is formed by actual intersection of rays.

1. A virtual image is not formed by actual intersection of rays.

2. It can be obtained on a screen.

2. It cannot be obtained on a screen.

3. It is always inverted.

3. It is always erect.

LAWS OF REFLECTIONS:

  1. The angle of incidence ( i ) is always equal to the angle of reflection ( r ).
    i.e. Ð i = Ð r
  2. The incident ray, the reflected ray, and the normal to the mirror at the point of incidence all lie in the same plane.

CHARACTERISTICS OF IMAGE FORMED BY A PLANE MIRROR:

The image formed by a plane mirror is

  1. virtual and erect.
  2. of the same size as the object.
  3. as far behind the mirror as the object is in front of the mirror.
  4. laterally inverted.

RULES FOR IMAGE FORMATION BY SPHERICAL MIRROR:

  1. The ray parallel to the principal axis, after reflection, passes through the principal focus of a concave mirror, or appears to pass through the principal focus of a convex mirror.
  2. A ray passing through the principal focus in a concave mirror, or a ray which is directed towards principal focus in a convex mirror, is reflected parallel to the principal axis.
  3. A ray passing through the centre of curvature in a concave mirror, or a ray which is directed towards centre of curvature in a convex mirror, is reflected back along its own path.
  4. A ray incident to the pole of a spherical mirror making an angle with the principal axis reflects along a path making an equal angle with the principal axis on the opposite side of the principal axis.