PHYSICSPropagation & Reflection Of Light

Light• Light was considered as mysterious thing in

olden days.• Light deals with luminous energy, energy

which causes the sensation of vision.• Light is brightness that comes from an

object producing light , called luminous body (sun).

• Light comes from atoms. Atoms that produce light have either gained energy by absorbing light from an other source or by being struck by other particles. It is this extra energy that causes an atom to give off light.

• Study of light and interaction of light and matter is known as optics.

Properties of Light

Rectilinear propagation.

Shadow formation

Reflection.

Refraction.

Diffraction.

Dispersion.

Polarization.

Interference.

Properties of Light

Shadow Formation= The straight rays of light passing the edges of non transparent( opaque) body, leave a sharp shadow of that body in the way of light.

Properties of Light

Rectilinear Propagation= Light travels in straight lines very fast.

Laser

Properties of Light

Reflection = when light strikes smooth shining surface it returns back into same medium.

Incident ray Reflected ray

Normal

Properties of Light

Refraction = When light enters from one transparent medium into another , it changes its path.

airglass

normal

incident ray

angle of refraction

angle of incidence

refracted ray

Properties of Light

Properties of Light

Diffraction = It is apparent bending of light waves around the obstacle in its path.

Dispersion = It refers to the break down of white light( sun light) into its constituent colours.

Properties of Light

Properties of Light Interference = It is the phenomenon that occurs

when two beams of light meet, to give brighter beam

(constructive interference) or to produce less bright beam( destructive interference).

Properties of Light

Polarization= It is the direction, the wave is vibrating in.

Plane-polarized waves

Plane-polarized waves 

Circularly polarized waves

The reflection of Mount Hood in Mirror Lake.

Double reflection: The sun is reflected in the water, which is reflected in the paddle.

Reflection Of LightWhen light traveling through one medium

strikes the surface of another medium(Mirror), part of it is returned back in the first medium in a particular direction, such phenomenon is called Reflection of Light

Regular Reflection Or Specular Reflection

When rays of light strike the smooth shining surface ( plane mirror) they are reflected in the same direction , it is called regular reflection. In it at different places of surface, the values of incident angle ( Li) are same.

Irregular Reflection Or Diffused Reflection

When rays of light strike rough surface(Earth), they are reflected in different directions, it is called irregular reflection. In it at different places of surface the value of incident angle(Li) are not same.

Laws Of Reflection Of Light

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

The angle of incident(li) is equal to the angle of reflection (Lr).

Position & Nature Of Image Formed By Plane Mirror

• In plane mirror image formed is of the same size as the object.

• Image is as far behind the mirror as the object in front of the mirror.

• Image is virtual and laterally inverted.

Applications Of Plane Mirror

• It is used as a looking glass.• In the field of medicine, it is used by

Dentists and Ophthalmic surgeons.• It is used in electric meters, in special

head lights, light microscopes, periscope and kaleidoscope.

Applications Of Plane Mirror

As looking glass Periscope

Kaleidoscope Microscope

Applications Of Plane Mirror

Ophthalmoscope

Electric Meter

Applications Of Plane Mirror

Plane Mirror Head Light

Pin Hole Camera

A pin hole camera is a simple camera without a lens and with aperture , effectively alight - proof box with a small hole in one side.

Light rays from an object pas through a small hole to form an inverted image , on semitransparent paper at the back of the box. It is also known as camera obscura ( dark room).

Pin Hole Camera

HoleImage

Semitransparent paper

Object

Types Of Mirror

Plane Mirror Curved Mirror Parabolic Mirror

Spherical Mirror

• A mirror having curve surface is termed as spherical mirror, being a part of large hollow mirror) or curved mirror.

Types Of Spherical Mirrors

• Spherical mirrors are classified into following two types, according to how they reflect light rays from a distant source.

Terms Used In Spherical mirror CP = Radius of curvature. C = Centre of curvature. PO = Principal axis. P = Pole of mirror. F = Focus of mirror. PF(f) = focal length of mirror. XY = Aperture of mirror.

Concave Mirror

Its reflecting surface caves inwards.It is converging mirror.It forms real image.Its focal length is taken positive ( +ve ).

Convex MirrorIts reflecting surface bulges

outwards.It is diverging mirror.It forms virtual image.Its focal length is taken negative (-ve ).

Uses Of Spherical Mirrors

Concave Mirrors=(1)These are used in search light, head light and flash light.(2)These are used as objective in Reflecting Telescopes.

(3) These are used as magnifiers.(4) These are used in solar heaters.

Reflecting Telescope

Uses Of Concave Mirror

Uses Of Concave Mirror

Head Lights

As Magnifier

Uses Of Spherical MirrorsConvex Mirror = These having vast

field vision are used as side mirrors in motor vehicles.

Uses Of Spherical Mirrors

Rules For Light Rays In concave Mirror

A. The ray of light C,this is reflected back through C.

B. The ray of light parallel to the principal axis, is reflected through F.

C. The ray of light through F, is reflected parallel to the principal axis.

Ray diagrams

Description Of An ImageTo describe an image, fallowing four aspects

need to be determined. Its location = Where it is in relation to the mirror. Its size =How big it is compared with the object. Its orientation = Where it is upright or upside down. Its nature = Where or not the image can be captured

on a screen.

Images Formed By concave Mirror

I. If object is placed beyond C.Its image will be formed near F ( out side the focus of mirror) the focus of mirror. Image will be real, inverted and smaller than the object.

II. If object is placed at C .Its image will be formed at C.image will be real, inverted and of same size as object.

Images Formed By concave Mirror

Images Formed By concave Mirror

III.If object is placed b/w C and F. its image will be formed out side the C. Image will be real, inverted and larger than object.

Images Formed By concave Mirror

IV. If object is placed inside the focus(F). Its image will be formed behind the mirror.Image will be virtual, upright and magnified.

Difference B/W Real & Virtual Image

Real Image• In it rays of light

actually pass through it.

• It can be obtained on screen.

• Its distance is shown with +ve sign.

• It is inverted.

Virtual Image

a) In it rays appear coming from the place of image.

b) It is only visible to eye and can not be obtained on screen.

c) Its distance is shown with –ve sign.

d) It is upright.

Magnification & Sign Conventions For spherical Mirrors

Optical magnification is the ratio between the size of image & size of object.

M = hi = q

ho p

M = Magnification, hi = Height of image , ho = Height of object.

Distance b/w concave mirror & image (q ) is taken +ve. Distance b/w convex mirror & image is taken –ve. Focal length of concave mirror ( f ) is taken +ve. Focal length of convex mirror is taken –ve .

Mirror Equation ( Concave Mirror)

Δ ABC and Δ OIC are similar.

AB/OI = BC/IC = p/q……………(i)

ΔABF and Δ FCD are similar.

AB/DC = BF/FC = BC – FC / FC = p - f / f……………..(ii)

Mirror Equation ( Concave Mirror)

Comparing I & ii

p/q = p – f / f B.C.M pf = pq – fq……….(iii)

Dividing both the sides of Eq:III with pqf.

Pf/pqf = pq/pqf = fq/pqf.

1/q = 1/f – 1/p or 1/f – 1/p = 1/q.

1/f = 1/p + 1/q( Mirror Equation).