# Light Reflection and Refraction Class 10 Notes Numericals

Class 10 Science Study Notes Chapter 10 : Life Processes are available here for students and teachers for education purpose.

Contents

## Class 10 Science Chapter 10 Light Reflection and Refraction

Class 10 Science Chapter 10 is “Light Reflection and Refraction” . This tenth chapter of science class 10 in NCERT Text Book is very useful for exam point of view. This chapter consists of the topics – light, reflection and refraction of light, mirror, lens , Image formation by Mirrors and Lens, Refractive Index, Power of Lens, etc

## Chapter 10 : Light Reflection and Refraction

### Light Reflection and Refraction Class 10 Notes ( Study Notes )

1. Light : Light is a form of energy that helps the living organisms to see the nearby areas

2. Reflection of Light : The bouncing back of Light after striking any surface(polished Surface) is known  as Reflection of Light.

3. Laws of Reflection
• Angle of Incident = Angle of Reflection
• The Incident ray , the reflected ray and the normal , all lie on the same plane.

4. Mirrors
• Objects which have a reflecting surface (due to which an image is formed) are known as Mirror.
• Plane Mirror : A Mirror which is straight and has no curves is known as Plane Mirror.
Example : Table Mirror at home (used to see ourselves)

5. Concave Mirror : Those mirrors whose reflecting surface are curved inward are known as Concave Mirror.
a) Uses of Concave Mirror:
• Concave mirror is used in torch
• Concave mirror is used in the vehicle’s headlamps
• Concave mirrors are used by dentists to see the teeth of the patients.
• Concave mirrors are used in solar furnace to produce heat.

6. Convex Mirror: Those mirrors whose reflecting surfaces are curved outward are known as Convex Mirrors
a) Uses of Convex Mirror : Convex mirrors are used as side mirrors in vehicle to see the  rear view.

7. Important terms related to Mirrors
a) Pole : The Centre point of the reflecting part of the spherical mirrors is known as the Pole
b) Principal Axis: An imaginary line which joins the two points namely, Pole and Centre of Curvature is known as Principal axis .
c) Principal Focus: The Point on Principle axis where all the incident rays coming parallel to the Spherical mirrors intersect the principal axis after reflecting from the Mirror Surface is known as Principal Focus.

d) Aperture :  The total length of the reflecting area of the Mirror is known as its Aperture.
e) Focal Length : The distance between the Pole and principal Focus is known as Focal Length. Focal Length is denoted by ‘f’.
f) Radius of Curvature : Centre of Curvature is defined as radius of the Spherical mirror whose is this mirror is a part. It measured as the distance between Centre of Curvature and Pole

8.) Sign Convention for Reflection
• All the distance are measured from the pole.
• Distance on right side of the pole are taken as +ve values.
• Distance on left side of the pole are taken as  -ve values(in calculation)
• Distance above the Principal axis (height) are taken as +ve values.
• Distance below the Principal axis (height) are taken as -ve values (in calculations).

9. Image Formation by Plane Mirror

10. Image Formation by Concave Mirror

11. Image formation by Convex Mirror

12. Refraction
a) Refraction of Light. : The bending of light when it passes from one medium to another is known as Refraction of Light.
b) Laws of Refraction
• The incident ray, the refracted ray and the normal , all lies on the same plane.
• Snell’s Law : The ration of sine of angle of incident to the sine of angle of refraction is always constant, for the particular colour of light and for a particular pair of media.
$$\frac{Sin \ i }{Sin \ r} \ = \ Constant \ = \ μ \$$

13. Refractive Index : Refractive Index is defined as the ratio of speed of light in medium 1 to the speed of light  in medium 2 . Mathematically , Refractive Index is given as follow:
n21   = $$\frac{Speed \ of \ Light \ in \ Medium \ 1}{Speed \ of \ Light \ in \ Medium \ 2}$$

15. Lens
a) Lens : Lens is defined as the transparent object which is bounded by the two spherical surfaces on each side.
b) Concave Lens : When a lens is bounded by the spherical surfaces which are curved inside , then such type of lens is known as concave lens.
c) Convex Lens  : When a lens is bounded by the spherical surfaces which are curved Outside , then such type of lens is known as convex lens.

16. Some Important Terms related to Lens
a) Principal Axis : And Imaginary line which passes through the Optical Centre and F1  and 2F1 .
b) Principal Focus : The point on Principal axis on which the incident rays (parallel to principal axis) intersect the principal axis after being refracted by the lens is known as Principal Focus
c) Focal Length : The distance of the Focus from the Optical Centre is known as the Focal length .

17. Image formation by Convex lens

18. Image formation by concave lens

19. Power of Lens : Power of Lens is defined as the reciprocal of the focal length of the Lens . The SI unit of Power is Dioptre (D).
$$\ P \ =\ \frac{1}{f}$$ $$\ P$$ : Power of Lens $$\ f \$$ : Focal Length of Lens

### Mathematical formulae used in this Chapter.

1. Mirror Formula
$$\frac{1}{f} \ = \ \frac{1}{u} \ + \frac{1}{v} \$$
Focal Length of the Mirror : $$\ f$$
Object Distance from Pole : $$\ u$$
Image Distance from the Pole : $$\ v \$$

2. Magnification (Mirror)
$$\ m \ = \frac{h’}{h} \ =\ – \ \frac{v}{u}$$
Magnification = height of image / height of object
$$\ m \ > \ 1 =$$ Image has been Magnified.
$$\ m \ < \ 1 =$$ Image has been diminished
$$\ m \ = \ 1 =$$ Image is of the same size as that of the Object.

3. Lens Formula
$$\frac{1}{f} \ = \frac{1}{v} \ – \ \frac{1}{u}$$
Focal Length of the lens : $$f$$
Object Distance from Optical Centre : $$u$$
Image Distance from the Optical Centre : $$v$$

4. Magnification ( Lens)
$$\ m \ = \frac{h’}{h} \ =\ \frac{v}{u}$$
Magnification = height of image / height of object
$$\ m \ > \ 1 =$$ Image has been Magnified.
$$\ m \ < \ 1 =$$ Image has been diminished
$$\ m \ = \ 1 =$$ Image is of the same size as that of the Object.

5. Power of Lens
$$\ P \ = \ \frac{1}{f}$$
$$P$$ : Power of Lens
$$f$$ : Focal Length of the lens

6. Power of Combined Lens
Total Power =  P1 ­+ P2  + P+ ….
P1  : Power of Lens 1
P2  : Power of Lens 2
P3  : Power of Lens 3