Light
Light
- Light is a form of energy which is responsible for the sense of sight.It enables to see things around us.
- Natural sources of light are Sun, fire etc.
- Man-made sources of light are tube lights, bulbs etc.
Light travels in a straight line
- Light is made up of packets of energy called photons which travel in a straight line at a very fast speed. Light can move through small apertures and holes and can change direction, but will always travel in straight lines.
Reflection
- Light, sound, water, electromagnetic waves may change their direction upon striking a surface. This is called reflection.
- Light waves get reflected while other waves may penetrate the surface.
- Light gets reflected easily by shiny surfaces like stainless steel plate, water, mirror etc.
- Polished and shiny surfaces act as a mirror due to light reflection capabilities.
Reflection by Plane Mirror
- Light falling on a plane mirror at an angle (Angle of incidence) gets reflected at the same angle (Angle of reflection) in other direction.
- When an object is placed in front of the mirror, an image of the object is formed by the mirror which appears to be behind the mirror.
- The image formed by a plane mirror is
- Erect (upright position)
- Of the same size as the object
- At the same distance as the object
- With right and left sides interchanged.
- The image formed cannot be obtained on a screen. If we place a screen (cardboard) in front or back of the mirror, the image will still can be seen only in the mirror and not the screen.
Spherical Mirror
- A curved shining surface of an object acts as a mirror.
- Most common types of curved mirrors are called spherical mirrors.
- Spherical mirrors are classified based on their reflective surface as one of two types, concave and convex.
- When a part of sphere is cut, the inside part is called the concave side, while the outside part is called the convex side.
- A common example is a stainless steel spoon whose inside part behaves as a concave and outer part behaves as a convex mirror.
Real and Virtual Image
- When an image is formed on a screen with the help of a mirror, it is called a Real Image. Similarly, an image which can’t be obtained on a screen with the help of a mirror, it is called Virtual Image.
- Concave and convex mirrors can be used to produce real as well as virtual images.
Concave Mirror
- A concave mirror produces a smaller, bigger and inverted image based on its distance from the object.
- When the distance between object and mirror is large, a small inverted virtual image is formed.
- As the object is brought closer, the image becomes larger.
- At a very close distance, the image is large and upright.
Applications of concave mirrors
- The application of concave mirrors lies in the fact that when it is brought closer to an object, an enlarged virtual image is obtained.
- Doctors use it for examining ears, nose, throat and eyes.
- Dentists use it for examining teeth and gums.
- Also, a concave mirror concentrates the light falling on it into a narrow beam. This is used in:
- Torches
- Car headlights
Convex Mirror
- A convex mirror generally produces anerect and smaller image of the object.
- Convex mirror produce virtual images of the objects spread over large area.
- Convex mirrors cannot produce real images.
Applications of convex mirrors
- Rear view mirrors of vehicles so that person driving is able to see most traffic behind him/her.
- As reflectors in street lamps to diverge light over a larger area.
- Used for making sun glasses and telescopes.
Lens
- A Lens is a type of mirror which refracts the light instead of reflection.Refraction is the bending of a light when it enters a medium. Here the medium is Lens.
- Lens are of various types but the two most important types are convex (on Bi-convex) and concave (or Bi-concave) lens
- Convex lens are thicker in middle than the edges whereas concave lens are thinner at the middle than at the edges
- Lenses are transparent and light can pass through them.
- Convex lens are also called convergent as they concentrate (bend inward) the light falling on it.
- Concave lens are also called divergent lens as they expand the light (bend outward) falling on it.
- Real images are formed using convex lens by placing them in between the object and the screen.
- Virtual images are also formed by convex lens which is erect and larger in size.
- Concave lens do not form real images. They only form virtual images which are always erect and smaller in size.
- Applications of lens include magnifying glass, telescopes, contact lens, cameras etc.
Sunlight
- The light rays emitted from the sun appear white but consists of 7 colours namely, red, orange, yellow, green, blue, indigo and violet. There are various phenomena and objects that can split these white rays into individual colour rays.
- Rainbow appears after or during rainfall due to the reflection, refraction and dispersion of suns light by the water droplets in the atmosphere.
- A Prism is a transparent optical object with polished surfaces which refracts light. It refracts the sunlight into the seven colours.
- A compact disc also displays fine lines of these 7 colours when sunlight falls on its shiny side.
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