Light energy
travels in straight line which called rays. And
The collection
of rays is called beam.
Opaque: If you cannot see through an object then the object is opaque
because opaque materials do not allow light to pass through them.
Translucent:We cannot clearly see
through the object then the object is translucent objects. Example tissue paper
etc.
Transparent object:The object through which we can see clearly. Example: air, glass, water.
There
are two laws of reflection (انعکاس).
First
law of light: The incident rays the reflected ray and the normal to the surface
all lie in the same plane.
Second
law of light: The angle of incidence rays is equal to the angle of reflection.
The law
of reflection was first described by Muslim scientist ibn-ul-haithem.
There
are two types of reflection.
Regular
Reflection: When parallel rays of light strike smooth and shining surface than
most of rays reflected with the same angle as that of angle of incidence.
Diffused
reflection (متغیر عکاسی): When parallel
rays of light strike rough and irregular surface then the reflected rays are
scattered(بکھرنا) in different direction.
Luminous object (برائٹ اشیاء): Luminous
objects give light of their own. ExampleSun, bulb, candle.
Non luminous object(غیر
برائٹ اشیاء): Non luminous objects can only be seen when light is reflected from them.
Example Moon, Earth etc.
A pinhole camera is a device that works on the principle that light travels in straight
line.
A Muslim scientist Al-Haithem invented the pinhole camera.
A small pinhole will give a sharp image while a large pinhole will give a blurred image.
A Periscope is a device which is used to watch
an object on other side of the barrier.
A simple periscope can be constructed by using two plane mirrors at
450
A Telescope is an instrument with help of which you can see distant object clearly.
A reflecting telescope has a concave mirror and a
plane mirror.
A Microscope is an instrument used to produce a large image of an object.
Kaleidoscope is an instrument or toy containing mirrors which make multiple reflections.
A kaleidoscope consists of a hollow tube containing two or more rectangular plane mirrors inclined to each other at certain angles.
Image depend upon the two
mirrors, if
a)The angle between the mirrors is 120o,two images of the objects are formed.
b)If the angles 900, thenthree images of the
object are formed.
c)If the angle is 600 then four images of the
object are formed.
The first kaleidoscope
came in to being in 1851, by Sir Davide Brewster who
belonged to Scotland.
Plane mirror:It is a mirror which is flat in shape and reflects
the light with the same angle as that of the angle of incident.
Image form by the plane mirror is literally inverts, virtual
and of same size.
