Chapter 7 : Reflection of Light

Reflection of Light

The return of light into the same medium after striking a surface.

Plane Mirror

A mirror that has one surface of glass plate polished to a high degree of smoothness and the other surface is silvered.

Concave Mirror

A spherical mirror where the inner surface is silvered, capable of converging light rays.

Convex Mirror

A spherical mirror where the outer surface is silvered, diverging light rays.

Laws of Reflection

1. The angle of incidence is equal to the angle of reflection.

2. The incident ray, reflected ray, and normal all lie in the same plane.

Real Image

An image that can be projected onto a screen, formed when light rays actually converge at a point. It is inverted.

Virtual Image

An image that cannot be projected onto a screen, formed when reflected rays appear to diverge from a point. It is erect.

Focal Length

The distance from the mirror's surface to its focus, it is half of the radius.

Centre of Curvature

The centre of the sphere of which the mirror is a part.

Principal Axis

The straight line joining the pole of the mirror and its centre of curvature.

Image Formation

The process where light rays diverge and appear to come from a point behind a mirror.

Magnification

The ratio of the length of the image to the length of the object.

Regular Reflection

Occurs when a beam of light strikes a smooth, polished surface such as a plane mirror.

Irregular Reflection

Occurs when light falls on a rough surface, resulting in scattered reflected rays.

Lateral Inversion

The interchange of the left and right sides in the image of an object in a plane mirror.

Sign Convention

• All distances are measured from the pole of the mirror are taken as origin.

• The distances measured along the principal axis in the direction of the incident light are considered positive, while those measured in the opposite direction are negative.

• The distances above the principal axis are positive, and those below it are negative.

Spherical Mirror Formula

1/f = 1/v + 1/u; relates object distance (u), image distance (v), and focal length (f).

Incident Ray

The ray of light that strikes the surface of a mirror.

Point of Incidence

The point where the incident ray strikes the surface of a mirror.

Reflected ray

The light ray obtained after the reflection from surface, in the same medium of incident ray.

Normal

The perpendicular drawn on the surface at the point of Incidence

Angle of Incidence

The angle between incident ray and normal .

Angle of Reflection

The angle between reflected ray and Normal

Plane of Incidence

The plane containing the incident ray and normal

Plane of Reflection

Plane containing reflected ray and normal.

Characteristics of Image formed by Plane mirror

It is upright, virtual, of the same size as the object, and laterally inverted.

If the angle between two mirrors is odd, the number of images formed are?

n = 360/angle, It is:

n (asymmetrical)

n-1 (symetrical)

If the angle between two mirrors is even, the number of images formed are?

n = 360/angle, it is n-1.

Images formed in a pair of mirrors placed parallel to each other

Infinite

Images formed by two mirrors kept perpendicular to each other

3 images

Uses of Plane Mirror

As a looking glass, In a optician’s room, Periscope etc

How are the mirrors kept in a periscope?

Two parallel plane mirrors, each inclined at 45 degrees

How are mirrors kept in a kaleidoscope?

3 plane mirrors inclined with each other at 60 degrees

Spherical Mirror

A reflecting surface which is a part of a sphere.

Radius Of Curvature

The radius of the sphere of which the mirror is a part.

Pole

the geometric centre of the spherical surface of mirror.

Aperture

The plane surface area of the mirror through which light rays enter and fall on the mirror.

Focus of Concave Mirror

It is a point on the principal axis through which the light rays incident parallel to it , pass after reflection from the mirror.

Focus of Convex Mirror

It is a point on the principal axis from which the light rays incidend parallel to the principal axis, appear to come, after reflection from the mirror.

Focal Plane

A plane passing through the focus which is normal to the principal axis.

Why does a light ray paasing through C return in the same direction?

Because a line joining any point on the surface of the mirror to C will be normal to the surface at that point.

Uses of Concave mirror

As a shaving mirror, As a reflector, as a doctors head mirror.

Uses of Convex Mirror

As a reflector in street lamps, As a rear view mirror.

How to identify if a mirror is a Concave mirror?

if the image is upright, magnified, and increases in size on small movements of the mirror away from the face.

How to identify if a mirror is a Convex mirror?

The image is diminished, upright, and decreases in size on small movement of the mirror away from the face.

How to identify if a mirror is a plane mirror?

The image is upright and diminished, it does not change in size by moving the mirror towards or away from the mirror.