SUBMITTED BYMUBASHIRA M

LIGHT - REFLECTION

WWW.DOWNVIDS.NET-Science - Light - Reflection - English.mp4

Reflection of light

The process of sending back the light rays which falls on the surface of an object – Reflection

The object having polished , shining surface reflects more light than object having unpolished, dull surface

Silver metal is good reflector of light

Laws of reflection of light

The incident ray , the normal to the mirror at the point of incidence and the reflected ray , all lie in the same plane.

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

It is a mirror which has the shape of a piece cut out of a spherical surface

Spherical mirror

Concave mirror It is a spherical mirror , whose reflecting surface is curved inward or faces towards the centre of the sphere.

CONVEX MIRROR It is a spherical mirror whose reflecting surface is curved outward

Types of spherical mirror

Pole (p) – centre point of the reflecting surface of a spherical mirror. It lies on the surface of the mirror.

Centre of curvature (C)- Centre point of the sphere , in which the reflecting surface of a spherical mirror forms a part of this sphere

Radius of curvature (R)- the radius of the sphere of which the reflecting surface of a spherical mirror forms a part.

Principal axis – Is a straight line passing through the pole and the centre of curvature of a spherical mirror.

Aperture- the diameter of the reflecting surface of spherical mirror

Terms of reflection

Pictorial representation

Focal length – the distance between the pole and the principal focus of a spherical mirror

A number of ray parallel to the principal axis are falling on a concave mirror and the reflected rays are all intersecting at a point on the principal axis of the mirror. This point is called the Principal focus of the concave mirror

Principal focus of the convex mirror – the reflected rays appear to come from a point on the principal axis

Principal focus and Focal length

Rays of light coming from infinity, making different angles with the principal axis get focused at different points.

The plane formed by these points is perpendicular to the principal axis and passes through the principal focus.

This plane is the principal axis

Focal plane

For a spherical mirror of small aperture,

The principal focus F lies midway - between the pole P and the centre of curvature C

The radius of curvature is found to be equal to twice the focal length

WWW.DOWNVIDS.NET-SPHERICAL MIRRORS.mp4

R = 2f

Ray diagram of spherical mirror

Path of incident ray Path of reflected ray

Concave mirror Convex mirror

Parallel to the principal axis Reflect through the focus Appears to come from the principal focus

Through the principal focus/ in the direction of the principal focus

Reflects parallel to the principal axis

Reflects parallel to the principal axis

Through the centre of curvature/ in the direction of centre of curvature

Reflects through the same path

Reflects through the same path

Ray falling obliquely at the pole

Reflects in such a way that the angle of incidence equal to the angle of reflection

Reflects in such a way that the angle of incidence equal to angle of reflection

Image formation by a Concave mirror for different position of the Object

Position of the object

Position of the image

Size of the image Nature of the image

At infinity At the focus F Highly diminished, point sized

Real and inverted

Beyond C Between F and C diminished Real and inverted

At C At C Same size Real and inverted

Between C and F Beyond C Enlarged Real and enlarged

At F At infinity Highly enlarged Real and enlarged

Between P and F Behind the mirror Enlarged Virtual and erect

Ray diagrams for the image formation by a concave mirror

Between P and F At F Between C and F

At C Beyond C At infinity

Commonly used in torches, search lights

Vehicle headlights to get powerful parallel beams of light

Often used as shaving mirror to see large image of the face

Dentists use concave mirror to see large images of the teeth of patients

large concave mirrors are used to concentrate sunlight to produce heat in solar furnace

USES OF CONCAVE MIRROR

Image formation by a Convex mirror

Position of the object

Position of the image

Size of the image Nature of the image

At infinity At the focus F, behind the mirror

Highly diminished, point sized

Virtual and erect

Between infinity and the pole P of the mirror

Between P and F, behind the mirror

Diminished Virtual and erect

Commonly used as rear-view mirror in vehicles, because

Enabling the driver to see traffic behind him to facilitate safe driving

They always give an erect, though diminished image

View as they are curved outward

Enable the driver to view much larger area than would be possible with a plane mirror

Uses of Convex mirror

Real image Virtual image

Inverted Virtual

Can be formed on the screen Cannot be formed on a screen

The distance towards the image and its height can be measured directly

The distance towards the image and its height cannot be measured directly

Real image Vs Virtual image

It is expressed as the ratio of the height of the image to the height of the object

It is usually represented by the letter

Magnification produced by a spherical mirror gives the relative extent to which the image of an object is magnified with respect to the object size

m = Height of the image / Height of the object

MAGNIFICATION

m = h’/h

m

Magnification m is also related to the object distance (u ) and image distance (v)

Object is taken to be positive as the object is usually placed above the principal axis

Height of the image should be taken as positive for virtual images, however taken as negative for real images

A negative sign in the value of the magnification indicates that the image is real

A positive sign in the value of the magnification indicates that the image is virtual

Magnification (m) = h’/h = - v/ u