Subject: Light class 7 notes
Introduction:-
Light enable us to see world.
Luminous objects:- Produce their own light. Example:- Sun.
Illuminous objects:- Donot produce their own light. Example:- chair.
Capable of reflecting light to our eyes coming from luminous objects.
Light:- A form of energy which enable us to see things around us.
Speed of light is 300000 km/s.
Light travels along straight lines.
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 off a ray of light into the same medium after striking a polished surface such as mirror.
Light reflected from an object reaches our eye and then we see things around us.
Incident ray:- Ray of light that strikes the surface.
Reflected ray:- Ray of light sent back be surface after reflection.
Normal:- Perpendicular to the surface at the point of incident. It is an imaginary line.
Angle of incidence:- Angle between Incident ray and normal.
Angle of reflection:- Angle between reflected ray and normal.
Laws of Reflection:- Incident ray, reflected ray and normal all lie on same plane.
Angle of incidence = Angle of reflection
Plane mirror:-Mirror with a flat reflective surface.
Real image:- Image is formed when reflected rays actually meet.
Can be obtained on screen.
Virtual image:- image formed when reflected rays appear to meet . It cannot obtained on screen.
Lateral inversion:- Left side of object appears right and vice versa. This is called lateral inversion.
Image formed by Plane mirror :-
Virtual and erect
Same size as that of object.
Image formed behind mirror.
Distance of image behind mirror is same as distance of object from the mirror.
Spherical mirror :-Mirror having spherical reflective surface.
Real image:- Image formed when reflected rays actually meet.
Virtual image:- Image formed when reflected rays appear to meet.
Lens:- Transparent optical medium bounded by two surfaces, at least one being spherical.
Types of lens:-
Convex lens:- Converging lens which is thicker at middle and thinner at edges.
Concave lens:- Diverging lens which is thinner at middle and thicker at edges.
Application of concave mirror:-
Used by doctor for examine eyes, ears, nose and throat.
Used by dentists to see enlarge image of teeth.
Reflector of torches, headlights of cars and scooter are concave in shape.
Sunlight:- White light made up of seven colours.
Prism:- Transparent element with three rectangular and two triangular surfaces is called prism.
Dispersion of light:- Splitting of light into its constituent colours. Example:- Rainbow
Spectrum:- Pattern of colours obtained after dispersion is called spectrum.
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