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LIGHTReflection of Light

Refraction of Light

Lenses

NATURE OF LIGHT

Light is a form of energy.

Light is a form of wave motion.

The way in which light radiates from its source is similar to the way in which ripples spread outwards across a pond.

NATURE OF LIGHT

Light travels at a speed of 3 x 108 m/s through empty space.

Light can be detected by human eye.

This speed is equivalent to travelling 7 times roundthe Earth in less than a second!

Light travels in straight lines.

Light travels in straight lines.

Light travels in straight lines.

EXPERIMENT TO DEMONSTRATE RECTILINEAR PROPAGATION 

Apparatus: 3 card board screens having small holes in their centers. Candle or lamp.

LIGHT RAYS

The path along which light energy travels is called a ray.

A light ray

A bundle of light rays is a beam of light.

Line represents the path along which light travels.Arrow represents the direction in which light travels.

LIGHT BEAMS

3 different types of light beams :

Parallel Beam : Light rays travels from very far away

Divergent Beam : Light rays from a point source (not far away)

Convergent Beam : Light rays meet at a point

REFLECTION OF LIGHT We can see

luminous objects: as they give off light which enters our eyes.Non-luminous objects: as they reflect light from a source to our eyes.

TERMS USED IN THE STUDY OF REFLECTION

A reflecting surface

Any shiny (smooth) surface. E.g a plane mirror

Symbol of a plane mirror

reflecting surface

TERMS USED IN THE STUDY OF REFLECTION

The incident ray

The ray that approaches the mirror.

incident ray

TERMS USED IN THE STUDY OF REFLECTION

The reflected ray

The ray that bounces off the mirror.

reflected rayincident ray

TERMS USED IN THE STUDY OF REFLECTION

The point of incidence

The point where the incident ray meets the mirror.

reflected rayincident ray

point of incidence

TERMS USED IN THE STUDY OF REFLECTION

The normal

The line that is perpendicular (at 90o) to the mirror.

normal

reflected rayincident ray

TERMS USED IN THE STUDY OF REFLECTION

The angle of incidence, i

The angle between the incident ray and the normal.

normal

reflected rayincident rayi

TERMS USED IN THE STUDY OF REFLECTION

The angle of reflection, r

The angle between the reflected ray and the normal.

normal

reflected rayincident rayi r

TERMS USED IN THE STUDY OF REFLECTION

LAWS OF REFLECTION

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

i = r

normal

reflected rayincident rayi r

LAWS OF REFLECTION

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

We always see all of them on the flat piece of surface.

LAWS OF REFLECTION

IMAGE IN A PLANE MIRROR

The image is virtual.

The image is upright.

The image formed has the same size as the object.

Image cannot be formed on the screen. Light rays do not meet at the image position.It is an imaginary image.

IMAGE IN A PLANE MIRROR

The image is as far behind the mirror as the object is in front of the mirror.

Object distance d1 = Image distance d2

d1d2

IMAGE IN A PLANE MIRROR

The image is laterally inverted (left-to- right inversion)

Left side of the object becomes the right side of the image.

APPLYING THE LAWS OF REFLECTION

To locate image formed in a plane mirror.

EYEO

RAY DIAGRAMS

Step 1 : Locate the image position.

EYE

I

O

RAY DIAGRAMS

Step 2 : Draw reflected rays (connect Image I to eye)

EYE

I

O

RAY DIAGRAMS

Step 2 : Draw incident rays. (connect object O to reflected rays)

EYE

I

O

To draw the mirror image of an object.

APPLYING THE LAWS OF REFLECTION

USING REFLECTION

Periscope

Mirror in meter

Optical testing

Other uses