# Physics Notes: Concept of Light (Optics) ## Physics Notes Concept of Light (Optics)

Introduction:
Light is a electromagnetic waves that is also transverse wave. Light is form o energy has wavelength between 3900 A° to 7800A°. Photoelectric effect, Compton Effect will be explained by using on the basis of the theory as proposed by Einstein. Its speed measure by Romer (1678 AD).
• Refractive index: it is a medium which is defined using the ratio of light in vacuum to the speed of light in medium. Refractive Index varies in various medium. In small refractive index velocity of light is large.
• Sun light takes 8 minutes to reach to earth.
Reflection of Light:

• One way to change the direction of light is to let it fall on a shiny surface.
• For example, a shining stainless steel plate or a shining steel spoon can change the direction of light.
• The distance between mirror to object and mirror to image is equal distance.
• Water surface is a medium of change light and its act like a mirror.
• When light falls in mirror its change its direction which is called reflection of light.
• The candle appears behind the mirror and we saw the image of the candle formed by the mirror. Here the candle is itself a object. This type of image is called erect. The image formed by a plane mirror where the formed same size compares object and image.
• Reflection of Light: when light moving through one medium and falls on the surface of another medium then a part of light returns back to the first medium, this activities of light in the first medium in compare to two medium is called reflection of light.

Special Mirror:

• Spherical mirror is the most common example of curved mirror.
• Concave mirror: the reflecting surface of a Spherical mirror is called concave mirror.
• Characteristics view of a Concave lens:
• Concave mirror can be set up the image can be small or large in size than the object.
• The image may be real or virtual.
• Concave mirror can be use as a shaving glass, as a reflector of the head lights of vehicle, in such light, doctors using concave mirrors cans examination eyes, ears, nose and throat. Concave mirrors are also used by dentists to see an enlarged image the teeth and also used in solar cookers.
• Convex mirror can formed object’s mirror spread over a large area. Its help the drivers to see the traffic behind them also used in sodium reflector lamp.
1. Lens: lens is a refractive transparent material of two surfaces which defined two surfaces of geometrical shape.
2. Basically Lens is two types: 1). Convex lens, 2). Concave lens. But we can divide it as below:
3. Convex lens: Those lenses which middle is thicker than its edge is called as convex lenses.
4. Concave lenses: Those which feel thinner in the middle than its edges are called concave lens.
5. Converging Lens: A concave lens converges the light generally falling on it. Therefore, it is called a converging lens.
6. Diverging lens: a concave lens diverges the light and is called diverging lens, here image formed by a concave lens is always virtual, erect and smaller in size than the object.

Image formed by spherical mirror

 Object Position Position of Image Real size of Image Image Nature Convex mirror At infinity At focus Highly diminished Virtual, erect In front of mirror Between pole and focus diminished Virtual, erect Concave Mirror At infinity At focus Highly diminished Real, inverted Between centre of curvature and infinity Between centre of curvature and focus Diminished Real, inverted At centre of curvature At centre of curvature Of same size Real, inverted Between centre of curvature and focus Between infinity and centre of curvature Enlarged Real, inverted At focus At infinity Highly enlarged Real, inverted Between focus and poles Behind the mirror enlarged Virtual, erect 