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:
- The angle of incidence ( i ) is always equal to the angle of reflection ( r ).
i.e. Ð i = Ð r - 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
- virtual and erect.
- of the same size as the object.
- as far behind the mirror as the object is in front of the mirror.
- laterally inverted.
RULES FOR IMAGE FORMATION BY SPHERICAL MIRROR:
- 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.
- 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.
- 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.
- 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.