- Light is a form of energy
- Light allows us to see different things around us.
- We see various objects with our eyes but our eyes only cannot help to see things
- Only when light coming from an object enters our eyes that we are able to see that object.
- The light may be of its own or may be reflected on the object from other source
- Luminous objects- The objects having their own light are called luminous objects
Example – sun, stars, electric bulb, tube-light, torch, candle and fire, etc.,
- Non- Luminous objects- The objects which donot have their own light are Non-luminous objects
Activity to show Light travels in straight lines.
- The fact that a small source of light casts a sharp shadow of an opaque object points to this straight-line path of light, usually indicated as a ray of light.
- Examples of opaque objects include wood, gold, cement, metal, some types of colored plastic, vegetation and so on.
Nature of Light
- Light is form of electromagnetic radiation and Non- mechanical wave(which donot require any medium for propagation)
- Light Exit dual nature both particle nature as well as wave nature
According to wave theory : Light consists of electromagnetic waves which do not require a material medium (like solid, liquid or gas) for their propagation
- Modern quantum theory of light states light is neither a ‘wave’ nor a ‘particle’
- Light travels at a speed of nearly 3 X 108 m/s in air or vacuum.
- Wavelength of visible light is 400 nm to 800 nm (4000 A° – 8000 A°) and the corresponding frequency is 7.5 x 1014 Hz to 3.75 x 1014 Hz
- Light travels along a straight line and this property is called the rectilinear propagation.
- The straight line is called a ray, and a bundle of rays is called a beam of light
Reflection of Light
- When light is incident on a surface, separating two media, a part of the light is bounced back to the first medium.This is known as reflection
- The process of sending back the light rays which fall on the surface of an object, is called reflection of light
- AB is the surface, PQ is the incident ray and QR is the reflected ray.
i = angle of incidence r = angle of reflection
Laws Of Reflection of Light
(i) The angle of incidence is equal to the angle of reflection, and
(ii) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
Reflection by a plane mirror
Image formed by plane mirror
- The image is virtual and erect.
- It is of the same size as that of the object.
- The distance between the object and the mirror is the same as that between the image and the mirror.
- It is laterally inverted.
Uses of Plane Mirrors
- Plane mirrors are used to see ourselves.
- Plane mirrors are fixed on the inside walls of certain shops (like jewellery shops) to make them look bigger.
- Plane mirrors are fitted at blind turns of some busy roads so that drivers can see the vehicles coming from the other side and prevent accidents.
- Plane mirrors are used in making periscopes.