NCERT SCIENCE 10 CH10 LIGHT - TOPIC 1.01 TO 1.04

THE PHYSICS CAFE                               

CHAPTER TEN
LIGHT - REFLECTION AND REFRACTION

 

1.01     Introduction - Theory of Light                                                                                     0

 

Particle nature of light: Light is supposed to be made up of particles and these particles travel in straight line

Wave theory of light: Light is supposed to be made up of particles and these particles travel like a wave.

Dual nature of light: At last, light is supposed to travel in straight line as well as like wave.

 

1.02 Light and Properties of Light                                                                                        1

 

Light is energy which helps us to see the things.

 

Properties of light

1.   Light travels in straight line.

2.   Light can travel without material medium.

3.   Speed of light in different medium (vacuum > air > water > glass > diamond)

4.   Speed of light is maximum in vacuum c = 3 x 10⁸ m/s.

5.   When light falls on any object some portion is absorbed by object(causes heating of object) and

·         Reaming portion is send back by object if object is Non transparent

·         Reaming portion is allowed to pass through the object if object is transparent.

 

1.03 Reflection of Light, Laws and Related terms*                                                                1

 

We will study two important cases in which light falls on objects.

Let light is coming from any source of light and if it falls on:

 

1. Non Transparent object – light can’t pass through the object so some light will be absorbed by the object and reaming will be send back by the surface of the object – this phenomenon of  “sending back of light by the surface of the object” is called Reflection of light

2. Transparent object – light can pass through the object so some light will be absorbed by the object and reaming will be allowed to pass through the object, during this light changes medium and get bends – this phenomenon of “bending of light when changes medium” is called Refraction of light

 

 

 

 Reflection of Light: The phenomenon of “sending back of light by the surface of the object” is called Reflection of light.

 

 

Related terms:

Incident ray: The light ray which is falls on the object.

Point of incidence: The point on the surface of object where light ray fall on the object

Reflected ray: The light ray which is send back by the object

Normal: Imaginary line perpendicular to surface of object at the point of incidence.

Medium separating surface: The surface where two different mediums meet then the surface is called medium separating surface

Incidence angle ∟i: Angle between incident ray and normal

Reflected angle ∟r: Angle between reflected ray and normal

 

Laws of Reflection: We fall light ray on different Non transparent objects, we found two things common for all objects are then called law of reflection

 

First Law of Reflection: Angle of incidence is always equal to angle of reflection

                                 ∟i = ∟r

Second Law of Reflection: Incidence ray, normal and reflected ray all must lie in same plane

Hint: Plane means a two dimensional surface like paper.

 

 

1.04 Plane mirror and its Properties and Uses                                                                     1

 

Plane mirror: A flat and smooth piece of glass which is silver metal polished from one side.

Hint: Silver metal is very good reflector of light, it sends back almost 95% light which fall on it. Aluminum is also used due to its low cost

 

Properties of Plane Mirror:

1. Virtual and Erect images are formed

2. Size (height) of image is always equal of size of object placed in front of mirror

3. Distance of object is always equal to the distance of image, from the mirror

4. Image formed will always be lateral inverted

Hint: Lateral inverted means left side of object becomes right side of image and vice versa)

 

Plane Mirror is mainly used to see one’s self

 

 

 

 

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