CBSE Class 10 Physics Revision Notes for Light - Reflection and Refraction

In CBSE Class 10, Physics is a combination of theoretical and practical knowledge. Physics can be one of the toughest subjects to understand. In the CBSE Class 10 Physics syllabus, there are crucial topics such as electricity, magnetic effects of electric current, refraction of light, etc. Through the Physical Practical Class 10 CBSE sessions, you dive deeper into how things work. TopperLearning presents study materials for CBSE Class 10 Physics which will help you to effectively prepare for your final examination. Our Physics study materials are prepared by subject experts and include video lessons, revision notes, question banks, sample papers and past years' question papers.

Knowledge of physics gained through theories and Science practicals for Class 10 CBSE Physics can be a stepping stone towards great career profiles such as a physicist or an inventor. Even if you do not want to pursue a career related to Physics, the concepts learned through your CBSE Class 10 Physics chapters can make you a smarter person.

To help you with Physics learning, we have prepared the best CBSE Class 10 Physics notes with concept videos. You will enjoy learning complex concepts with ease using our video lessons created by our Physics experts. Additionally, practice the questions from our CBSE Class 10 Physics Question Bank and sample papers to face your Physics exam with full confidence.

All these help students to score well in the examination. Our study materials contain educational resources which will help you to gain a better understanding of Physics. The content is revised from time to time following the latest guidelines of the CBSE syllabus. Additionally, we have introduced an ‘Ask the Expert’ facility, where all Physics doubts are instantly resolved by our subject matter experts. Students will also be able to understand all the difficult concepts by referring to our textbook solutions (such as NCERT and RD Sharma textbook solutions) which are free of cost. We are confident that students will find our learning materials helpful to achieve greater amount of success in the CBSE Class 10 examination.  

 

 

Read  more

Light – Reflection and Refraction 

 

Reflection of Light

  • Reflection is the phenomenon of bouncing back of light into the same medium on striking the surface of any object. 
  • Laws of Reflection
  • First law: The incident ray, the normal to the surface at the point of incidence and the reflected ray, all lie in the same plane. o
  • Second law: The angle of reflection (r) is always equal to the angle of incidence (i). ir

 

  • The image formed by a plane mirror is always 
  •  virtual and erect 
  • of the same size as the object 
  •  as far behind the mirror as the object is in front of it 
  •  laterally inverted 
 
  • Spherical mirrors are of two types:
  • Convex mirrors or diverging mirrors in which the reflecting surface is curved outwards. 
  • Concave mirrors or converging mirrors in which the reflecting surface is curved inwards.
  • Some terms related to spherical mirrors:
  • The centre of curvature (C) of a spherical mirror is the centre of the hollow sphere of glass, of which the spherical mirror is a part. 
  • The radius of curvature (R) of a spherical mirror is the radius of the hollow sphere of glass, of which the spherical mirror is a part.
  • The pole (P) of a spherical mirror is the centre of the mirror.
  • The principal axis of a spherical mirror is a straight line passing through the centre of curvature C and pole P of the spherical mirror. 
  • The principal focus (F) of a concave mirror is a point on the principal axis at which the rays of light incident on the mirror, in a direction parallel to the principal axis, actually meet after reflection from the mirror. 
  • The principal focus (F) of a convex mirror is a point on the principal axis from which the rays of light incident on the mirror, in a direction parallel to the principal axis, appear to diverge after reflection from the mirror. 
  • The focal length (f) of a mirror is the distance between its pole (P) and principal focus (F). 
  • For spherical mirrors of small aperture, R = 2f.

  • Sign Conventions for Spherical Mirrors
    According to New Cartesian Sign Conventions,
  • All distances are measured from the pole of the mirror. 
  • The distances measured in the direction of incidence of light are taken as positive and vice versa.
  • The heights above the principal axis are taken as positive and vice versa. 
  • Rules for tracing images formed by spherical mirrors
    Rule 1: A ray which is parallel to the principal axis after reflection passes through the principal focus in case of a concave mirror or appears to diverge from the principal focus in case of a convex mirror.



    Rule 2:
    A ray passing through the principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror emerges parallel to the principal axis after reflection.



    Rule 3:
    A ray passing through the centre of curvature of a concave mirror or directed towards the centre of curvature of a convex mirror is reflected back along the same path.



Rule 4: A ray incident obliquely towards the pole of a concave mirror or a convex mirror is reflected obliquely as per the laws of reflection. 
 
 
 
 
 
  • Image formation by a concave mirror
  • Ray Diagrams 




 
 
 
 
 
 
  • Characteristics of images formed 
 
Position of object Position of image Size of image  Nature of image
At infinity At focus F Highly diminished Real and inverted
Beyond C  Between F and C Diminished Real and inverted
At C At C Equal to size of object Real and inverted
Between C and F Beyond C Enlarged Real and inverted
At F At infinity Highly enlarged Real and inverted
Between F and P Behind the mirror Enlarged Virtual and erect
 
 
  • Image formation by a convex mirror
  • Ray Diagrams


  • Characteristics of images formed 

Position of object Position of image Size of image  Nature of image
At infinity At focus F behind the mirror Highly diminished, point sized  Virtual and erect
Anywhere between infinity and the pole of the mirror  Between P and F behind the mirror Diminished Virtual and erect




  • Mirror Formula
    The object distance (u), image distance (v) and focal length (f) of a spherical mirror are related as begin mathsize 11px style 1 over straight u plus 1 over straight v equals 1 over straight f end style

  •  Linear Magnification (m) produced by a spherical mirror is

     begin mathsize 11px style straight m equals fraction numerator size space of space image space left parenthesis straight h 2 space right parenthesis over denominator size space of space object space left parenthesis straight h 1 space right parenthesis end fraction equals negative fraction numerator image space distance space left parenthesis straight v right parenthesis over denominator object space distance space left parenthesis straight u right parenthesis end fraction end style 
    m is negative for real images and positive for virtual images.

Refraction of Light
  • The phenomenon of change in the path of a beam of light as it passes from one medium to another is called refraction of light. 
  • The cause of refraction is the change in the speed of light as it goes from one medium to another. 

  • Laws of Refraction 
  • First Law: The incident ray, the refracted ray and the normal to the interface of two media at the point of incidence, all lie in the same plane. 
  • Second Law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media.
    begin mathsize 11px style sini over sinr equals constant equals 1 straight n 2 end style 
    This law is also known as Snell’s law.
    The constant, written as  1n2 is called the refractive index of the second medium (in which the refracted ray lies) with respect to the first medium (in which the incident ray lies).

  • Absolute refractive index (n) of a medium is given as

     begin mathsize 11px style straight n equals fraction numerator speed space of space light space in space vacuum over denominator speed space of space light space in space the space medium end fraction equals straight c over straight v end style
  • When a beam of light passes from medium 1 to medium 2, the refractive index of medium 2 with respect to medium 1 is called the relative refractive index, represented by 1n2 , where
    begin mathsize 11px style 1 straight n 2 equals fraction numerator straight n 2 over denominator straight n 1 end fraction equals fraction numerator straight c divided by straight v 2 over denominator straight c divided by straight v 1 end fraction equals fraction numerator straight v 1 over denominator straight v 2 end fraction end style

    Similarly, the refractive index of medium 1 with respect to medium 2 is 
    begin mathsize 11px style 2 straight n 1 equals fraction numerator straight n 1 over denominator straight n 2 end fraction equals fraction numerator straight c divided by straight v 1 over denominator straight c divided by straight v 2 end fraction equals fraction numerator straight v 2 over denominator straight v 1 end fraction end style

    begin mathsize 11px style ⇒  1 straight n 2 space cross times space 2 straight n 1 equals 1

or space comma space 1 straight n 2 space equals fraction numerator 1 over denominator 2 straight n 1 end fraction
end style

  • While going from a rarer to a denser medium, the ray of light bends towards the normal.
  • While going from a denser to a rarer medium, the ray of light bends away from the normal. 

  • Conditions for no refraction
  • When light is incident normally on a boundary.
  • When the refractive indices of the two media are equal.
  • In the case of a rectangular glass slab, a ray of light suffers two refractions, one at the air–glass interface and the other at the glass–air interface. The emergent ray is parallel to the direction of the incident ray.



  • Convex lens or converging lens which is thick at the centre and thin at the edges.
  • Concave lens or diverging lens which is thin at the centre and thick at the edges.

 
  • Some terms related to spherical lenses: 
  • The central point of the lens is known as its optical centre (O).
  • Each of the two spherical surfaces of a lens forms a part of a sphere. The centres of these spheres are called centres of curvature of the lens. These are represented as C1 and C2
  •  The principal axis of a lens is a straight line passing through its two centres of curvature. 
  •  The principal focus of a convex lens is a point on its principal axis to which light rays parallel to the principal axis converge after passing through the lens. 
  • The principal focus of a concave lens is a point on its principal axis from which light rays, originally parallel to the principal axis appear to diverge after passing through the lens. 
  • The focal length (f) of a lens is the distance of the principal focus from the optical centre. 
 
  • Sign Conventions for Spherical Lenses 
    According to New Cartesian Sign Conventions, 
  • All distances are measured from the optical centre of the lens.
  • The distances measured in the direction of incidence of light are taken as positive and vice versa. 
  • The heights above the principal axis are taken as positive and vice versa. 
 
  • Rules for tracing images formed by spherical lens
    Rule 1:
    A ray which is parallel to the principal axis, after refraction passes through the principal focus on the other side of the lens in case of a convex lens or appears to diverge from the principal focus on the same side of the lens in case of a concave lens.




Rule 2: A ray passing through the principal focus of a convex lens or appearing to meet at the principal focus of a concave lens after refraction emerges parallel to the principal axis. 
 



Rule 3: A ray passing through the optical centre of a convex lens or a concave lens emerges without any deviation.




  • Image formation by a convex lens 
  • Ray Diagrams 













  •  Characteristics of images formed 
Position of object Position of image Size of image  Nature of image
At infinity At focus F1 Highly diminished Real and inverted
Beyond 2F1 Between F2 and 2F2 Diminished Real and inverted
At 2F1 At 2F2 Equal to size of object Real and inverted
Between F1 and 2F1 Beyond 2F2 Enlarged Real and inverted
At focus F1 At infinity Highly enlarged Real and inverted
Between F1 and o

Beyond F1 on the same side as the object

Enlarged Virtual and erect


  • Image formation by a concave lens
  • Ray Diagrams
 

  • Characteristics of images formed 
Position of object Position of image Size of image  Nature of image
At infinity At focus F1 Highly diminished Virtual and erect
Between infinity and O Between focus F1 and O Diminished Virtual and erect


 
  • Lens Formula Object distance (u), image distance (v) and focal length (f) of a spherical lens are related as begin mathsize 11px style 1 over straight u minus 1 over straight v equals 1 over straight f end style
  •  Linear Magnification (m) produced by a spherical lens is

     begin mathsize 11px style text m= end text fraction numerator size space of space image space left parenthesis straight h 2 space right parenthesis over denominator size space of space object space left parenthesis straight h 1 space right parenthesis end fraction equals fraction numerator image space distance space left parenthesis straight v right parenthesis over denominator object space distance space left parenthesis straight u right parenthesis end fraction end style 

m is negative for real images and positive for virtual images.

  • Power of a lens 
  • Power of a lens is the reciprocal of the focal length of the lens. Its S.I. unit is dioptre (D).
     P (dioptre) f metre 
  • Power of a convex lens is positive and that of a concave lens is negative. 
  • When several thin lenses are placed in contact with one another, the power of the combination of lenses is equal to the algebraic sum of the powers of the individual lenses. P = P1 + P2 + P3 + P4 +.......... 

Why choose TopperLearning’s CBSE Class 10 study materials?

On TopperLearning, your student dashboard gives you access to CBSE Class 10 Chapter-wise Physics lesson explanation as per the latest CBSE Grade 10 syllabus. We have more than 2000 questions (with answers) and several sample papers to help you prepare for Physics Class 10 Board exam.

You don’t need to compile notes from various sites online. With your TopperLearning account, you get complete access to NCERT Solutions, notes, tests, MIQs and more. In case, you have doubts related to the Physics CBSE Class 10 topics, you can ask an expert and our expert will clear your doubts within 24 hours.

We aim to develop your interest in learning Physics by making it enjoyable through videos and more. If you enjoy learning the subject, you can score better marks and get the opportunity to become a CBSE topper.