Class 7 chap 15 light

 Chap 15 Light notes

Introduction:-

Light is a form of energy which enable us to see world.

Speed of light = 30000Km/sec

Travels along a straight path.

Luminous objects:- Produce their own light .

Eg -- > Sun

Illuminous objects:- Donot Produce their own light . Eg:- Chair

Capable of reflecting light to our eyes coming from luminous objects.

Uses of Light:- Images formed by Mirror and lens

Rainbow formation

Ray of light:- Straight line path of light is called ray of light.

Beam of light:- Bunch of rays of light is called beam of light.

Reflection of light:-

Bouncing back of ray of light into the same medium after striking a polished surface such as mirror is called reflection of light.

Incident ray :- Ray of light that strike the surface.

Reflected ray :- Ray of light sent back by the surface after reflection.

Normal:- Perpendicular to the surface at the point of incident . It is an imaginary line.

Angle of incidence= angle between the Incident ray and normal.

Angle of reflection= Angle between the reflected ray and normal.

Law of reflection:- 

1. Angle of incidence= angle of reflection

2. Incident ray, reflected ray and the normal all lie on the same plane.

Types of mirror:- two types

1. Plane mirror

2. Spherical mirror

Plane mirror:- mirror with a flat reflective surface.

Characteristics of image formed by plane mirror:-

1. Virtual and erect image.

2. Same size as that of object.

3. Image formed behind mirror.

4. Distance of the image behind mirror is same as distance of object from mirror.

Virtual image:- Image formed when reflected rays appear to meet. It can't obtained on screen.

Real image:-Image formed when reflected rays actually meet. It can obtained on screen.

Lateral inversion:- In mirror left appears right and right appears left . This is called lateral inversion.

Spherical mirror:- Mirror having spherical reflecting surface.

Two types :-

1. Convex mirror 

2. Concave mirror

CONCAVE MIRROR:- mirror whose reflecting surface is curved inward. It is a converging mirror.

CONVEX MIRROR:- Mirror whose reflecting surface is curved outward. It is a diverging mirror.

Use of Convex mirror:- 

1. Can use as rear view mirror to get wider field view to help driver to see traffic behind them.

Used of concave mirror:-

1. Doctor use concave mirror for examining eyes, nose, ears and throat.

2. Dentists use concave mirror to see enlarge image of teeth.

3. Reflectors of torches, headlights of cars and scooters are concave in shape.

Lens:- Transparent optical medium bounded by two surfaces at least one being spherical is called lens.

Types of lens:- 

1. Convex lens( converging lens)

Thicker at middle and thinner at edges

2. Concave lens( diverging lens)

Thicker at edges and thinner at middle.

Uses:-

1. Magnifying glass.(Convex lens)

2. Used in Spectacles, telescopes and microscopes.

Sunlight:- It is a white light that is made up of seven colours.

Prism:- Transparent element with three rectangular and two triangular surface.

Dispersion of light:- 

Splitting of white light into its constituent colours is called dispersion of light. For example :- rainbow is formed when sunlight split into its 7 coloured band (VIBGYOR)

This pattern of colour obtained is called spectrum.