Chapter 16 Light Class 8 Notes | EduRev

Science - Short Notes for Class 8th

Created by: Sushil Solanki

Class 8 : Chapter 16 Light Class 8 Notes | EduRev

 Page 1


Chapter 16 – Light  
Light – A form of energy that helps up to see things. A dark room has no light, so we are unable to see 
anything. 
Reflection – The bouncing back of light after hitting a surface is called reflection. 
Dispersion – The scattering of light into its colors is known as dispersion. For e.g. the sunlight disperse into its 
seven color in a rainbow. 
Laws of reflection: 
Incident ray – the ray of light that falls on a surface is called incident ray 
Reflected ray – The ray of light that comes back from the surface after reflection is called the reflected ray.  
Normal – The line drawn at the point of hitting of incident and reflected ray making an angle of 90
0
 with the 
surface is called the normal. 
 
 
 
 
 
            Fig. Reflection of a light ray 
Angle of incidence – The angle formed between the incident ray and the normal is called the angle of 
incidence. It is denoted by ‘i’. 
Angle of reflection – The angle formed between the reflected ray and the normal is called the angle of 
reflection. 
1
st
 Law of reflection – The angle of incidence is equal to the angle of reflection. 
 
 
 
 
   Fig. Angle of incidence (i) and angle of reflection (r) 
            i  =      r  
 
2
nd 
Law of reflection – The incident ray, reflected ray and the normal lie on the same plane. 
Lateral inversion – The phenomenon in which right of an image appears left and the left appears right is 
known as lateral inversion.  
Page 2


Chapter 16 – Light  
Light – A form of energy that helps up to see things. A dark room has no light, so we are unable to see 
anything. 
Reflection – The bouncing back of light after hitting a surface is called reflection. 
Dispersion – The scattering of light into its colors is known as dispersion. For e.g. the sunlight disperse into its 
seven color in a rainbow. 
Laws of reflection: 
Incident ray – the ray of light that falls on a surface is called incident ray 
Reflected ray – The ray of light that comes back from the surface after reflection is called the reflected ray.  
Normal – The line drawn at the point of hitting of incident and reflected ray making an angle of 90
0
 with the 
surface is called the normal. 
 
 
 
 
 
            Fig. Reflection of a light ray 
Angle of incidence – The angle formed between the incident ray and the normal is called the angle of 
incidence. It is denoted by ‘i’. 
Angle of reflection – The angle formed between the reflected ray and the normal is called the angle of 
reflection. 
1
st
 Law of reflection – The angle of incidence is equal to the angle of reflection. 
 
 
 
 
   Fig. Angle of incidence (i) and angle of reflection (r) 
            i  =      r  
 
2
nd 
Law of reflection – The incident ray, reflected ray and the normal lie on the same plane. 
Lateral inversion – The phenomenon in which right of an image appears left and the left appears right is 
known as lateral inversion.  
Diffused or irregular image – A type of image formed when the parallel rays of light are not reflected 
parallely due to unevenness in the surface. E.g. image formed on a cupboard. 
 
 
 
  
 
Fig. Diffused image 
 
Regular image – Reflection by a smooth surface such as mirror in which the parallel light rays are reflected 
parallely.  
 
 
    
 
 
     
                                    Fig. Regular image  
 
Multiple images – Light rays once reflected can be reflected again by another mirror. This leads to the 
formation of another image on the other mirror. E.g. the image of your head (from behind) formed in the mirror 
kept in front of you. 
Application of multiple image – Periscope and Kaleidoscope.  
     Periscope is used in submarines to see out of the submarine. 
     Kaleidoscope is used to colorful light patterns.  
 
 
 
 
 
 
Fig. Structure of eye  
 
Page 3


Chapter 16 – Light  
Light – A form of energy that helps up to see things. A dark room has no light, so we are unable to see 
anything. 
Reflection – The bouncing back of light after hitting a surface is called reflection. 
Dispersion – The scattering of light into its colors is known as dispersion. For e.g. the sunlight disperse into its 
seven color in a rainbow. 
Laws of reflection: 
Incident ray – the ray of light that falls on a surface is called incident ray 
Reflected ray – The ray of light that comes back from the surface after reflection is called the reflected ray.  
Normal – The line drawn at the point of hitting of incident and reflected ray making an angle of 90
0
 with the 
surface is called the normal. 
 
 
 
 
 
            Fig. Reflection of a light ray 
Angle of incidence – The angle formed between the incident ray and the normal is called the angle of 
incidence. It is denoted by ‘i’. 
Angle of reflection – The angle formed between the reflected ray and the normal is called the angle of 
reflection. 
1
st
 Law of reflection – The angle of incidence is equal to the angle of reflection. 
 
 
 
 
   Fig. Angle of incidence (i) and angle of reflection (r) 
            i  =      r  
 
2
nd 
Law of reflection – The incident ray, reflected ray and the normal lie on the same plane. 
Lateral inversion – The phenomenon in which right of an image appears left and the left appears right is 
known as lateral inversion.  
Diffused or irregular image – A type of image formed when the parallel rays of light are not reflected 
parallely due to unevenness in the surface. E.g. image formed on a cupboard. 
 
 
 
  
 
Fig. Diffused image 
 
Regular image – Reflection by a smooth surface such as mirror in which the parallel light rays are reflected 
parallely.  
 
 
    
 
 
     
                                    Fig. Regular image  
 
Multiple images – Light rays once reflected can be reflected again by another mirror. This leads to the 
formation of another image on the other mirror. E.g. the image of your head (from behind) formed in the mirror 
kept in front of you. 
Application of multiple image – Periscope and Kaleidoscope.  
     Periscope is used in submarines to see out of the submarine. 
     Kaleidoscope is used to colorful light patterns.  
 
 
 
 
 
 
Fig. Structure of eye  
 
Function of various parts of eye 
a. Cornea – Cornea is the outermost transparent and tough part of the eye. It protects the eye from 
accidental damage. 
b. Iris – iris is the muscular structure that surrounds the lens. It give color to the eye and controls the 
amount of light entering the eye. 
c. Pupil – the area between the iris muscles from where the light enters the eyes 
d. Lens – a convex lens is present in the eye and it focuses the light into the eye on the retina. 
e. Retina – retina is the screen where the image is formed. 
a. Rod cells – are present in the retina and helps to see in dim light. 
b. Cone cells – help to see in bright light. 
f. Optic nerve – the optic nerve carry the signals of the image in electrical form to the brain. 
 
Blind spot – the part at the meeting point of retina and optic nerve where there are no sensory cells and 
the image cannot be formed is called the blind spot.  
 
Taking care of the eye 
a. Use specks if advised. 
b. Avoid working in too much or too little light. 
c. Do not rub your eyes with hands. 
d. Wash eyes regularly. 
e. Read from proper distance. 
f. Do not look directly at the sun. 
Visual aids  
The instrument of methods that help in to perceive or understand things that can be seen. 
a. Non optical aids – Visual aids that uses sense of touch or hearing, electronic aids and visual aids to help 
a person see or understand clearly. E.g. Braille system, audio CDs etc. 
b. Optical aids – Visual aids that uses a combination of lenses are called optical aids. E.g. contact lens, 
magnifiers and telescope. 
 
Braille System 
It is a system used by visually challenged people to read languages by sense of touch. Braille code is written in 
forms of dots, which are engraved on a surface and can be felt by hand. The various patterns of these dots can 
be used to identify various characters, symbols and letters.  
 
 
 
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