CHAPTER 10 LIGHT REFLECTION AND REFRACTION(CBSE CLASS 10)

Chapter 10

 LIGHT REFLECTION AND REFRACTION

Laws of Reflection 

• The angle of incidence is equals to the angle of reflection .
• The incident ray the normal to the mirror at the point of the incident and the reflected ray all lie  in the same plane at the same point.

Spherical Mirrors 

• concave mirror :-A spherical mirror whose reflecting surface curved  inverd that is faces towards the centre to the mirror known as concave mirror
  

• convex mirror :- A  spherical mirror whose reflecting surface is curved out word is called a convex mirror

Pole :- the centre of reflecting surface of a spherical mirror is a point called the pole it lies on the surface of mirror and it represented by P.

Centre Of Curvature :- the reflecting surface of a spherical mirror form a part of sphere this sphere has a Centre known as centre of curvature at represented by the letter C

Note:-

Centre Of Curvature Of A Concave Mirror lies in front of it and of the convex it lies behind the mirror

Radius Of Curvature :- the radius of the  sphere of which the reflecting surface of a spherical mirror form a part is called a radius of curvature it represented by the capital R 

Principal Axis :- the line passing through the pole and the centre of curvature is known as principal Axis

Focus:- when parallel rays coming from infinite reflected from the concave mirror and all the ray converge at a point known as principal focus of concave mirror 

focus of convex mirror it lies behind the reflecting surface of the convex mirror

Focal Length :- the distance between pole and the principal focus of spherical mirror is called the focal length it is represented by small f.

Relation between radius of curvature and focal length

R=2f

Image Formation By Spherical Mirrors 

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At Infinity	At The Focus F	Highly Diminished,Point Size	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
Beyond c	between f and C	diminished	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At C	At C	same size	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
between C and F	beyond c	enlarged	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At F	At  infinity	highly enlarged	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
between p and F	behind the mirror	enlarged	virtual and erect

Uses Of Concave Mirror 

• used in torch search light and vehicle headlight
• shaving mirror
• dentist
• large concave mirror are used to concentrate sunlight to produce heat in solar furnance

Image Formation Of Concave Mirror

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At infinity	at the focus f behind the mirror	highly diminished. Point Sized	virtual and erect

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
between infinity and we pole p of the mirror	between p and F behind the mirror	diminished	virtual and erect

Uses Of  Convex Mirror 

convex mirror commonly used as rear view image of vehicle mirror

Sign Convention For Reflection By Spherical Mirror

Mirror Formula 

v:- distance of image from pole

u:-you distance of object from pole

f:-distance of focust from pole

Magnification 

height of the image    /  height of the object

Refraction Of Light

• light travels in a straight line
• when light travel in a transparent medium it  strike obliquely at the surface of another transparent medium
• a part of light returns back into the same medium for obeying  the law of reflection is called reflectied   light
• the remaining part of light passes Into The Other medium and travel in a direction different from it initial direction and is called refracted light
• The phenomenon of bending of light at the surface separating from one medium to another is called refraction of light.

Laws Of Refraction 

• The incident ray the reflected ray and the normal at the point of incidence all lie in the same plane
• snell's law  

Refractive Index 

it is the ratio of the Sine of the incident angles and the sine of the refrected angle

Refraction Of Light Through A Rectangular Glass Block

The Literal Displacement Depends On 

• the thickness of the glass blocks
• the angle of incidence
• the refractive index of glass and also the wavelength of light used

Refraction Through A Lens 

Lens 

A lens is a transparent refracting medium bounded to curved surface which are generally spherical

Centre Of Curvature 

the centre of the sphere whose part is the lens surface is called the centre of curvature of that surface of the lens

Radius Of Curvature 

the radius of the sphere whose part is the lens surface is called the radius of curvature of that surface of lens

Principal Axis 

it is the line joining the centre of curvature of the two surface of the lens

Optical Centre 

it is a point on the principal axis of the lens such that a Ray of light passing through this point emerges parallel to its  direction of incidence

Ray diagram to locate the image formed by a convex lens

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At Infinity	At F2	Highly Diminished. Point Sized	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
Beyond 2f1	Between The Focus And Centre Of Curvature	Diminished	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At 2f	At The Centre Of Curvature	Same Size	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
Between F And 2f	Beyond The Centre Of Curvature	Enlarged	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At The Focus F	At Infinity	Highly Enlarged	Real And Inverted

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
Between The Focus F And Optical Centre C	Behind The Object	Enlarged	Virtual And Erect

Ray diagram to locate the image formed by a concave  lens

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
At Infinity	At The Focus	Highly Dimnished Point Sized	Virtual And Erect

Position Of The Object	Position Of The Image	Size Of Image	Nature Of The Image
Between The Infinity And Optical Centre	Between Focus And Optical Centre	Diminished	Virtual and Erect

Difference Between Real And Virtual Image 

Real image	Virtual image
Real Image Is Formed Due To Actual Intersection Of The Ray Reflected By The Lens	A Virtual Image Is Formed When The Ray Reflected By The Lens Appear To Meet If They Produce Backward
A Real Image Can Be Obtained On A Screen	A Virtual Image Cannot Be Obtained On A Screen
A Real Image Is Inverted With Respect Of The Object	The Virtual Image Is Erect With Respect To The Objects

Power Of Lens 

the deviation produced by a lens in the path of rays refrected through it is a measure of its power

power of lens (in D) 

Unit-------> Dioptre

• a lens has a power of 1 diopter if its focal length is 1 m = 100 cm
• depending on the direction in which a light ray is directed by the lens its power is positive or negative
• convex lens direct  a ray  towards the centre( converging ) :-positive
• concave lens direct  a ray  away from the centre( diverging ):- negative