~ Introduction
We see many objects around us in the 🌎 World
However, we are unable to see anything or any
object in a dark room. On lightining up the room,
things become visible. light is a form of energy
which enables us to see.
~ properties of light
• It is an electromagnetic wave, it does not required any medium.
• Light tends to travel in straight line.
• It has dual nature. (Particle wave)
• It makes(casts) shadows.
• Speed of light in vacuum air 3×10/8ms/-1.
~ IMPORTANT TERMS RELATED TO LIGHT
1. A Source of light🚨 : is an object, which emits light. For example, sun, electric
bulb, candles, e.t.c. some sources of light
are natural and some are man-made
or artifical. SUN is the most important
natural natural source of light for us.
Source of light are of two types : Luminous and non-luminous.
• LUMINOUS SOURCE : All the sources (objects)
which emit their own light are called LUMINOUS
SOURCES. For example, the sun, the stars, electric
lamp, candle, etc. Are luminous source of LIGHT.
• Non-luminous source : All sources
(objects) which do not 🚫 emit their own
light and become visible by merely
reflecting the light falling on them are
called NON-LUMINOUS SOURCES. For example, a chair, a table, a book, etc,. are
non-luminous source of light. EVEN THE
MOON IS A NON-LUMINOUS SOURCE AND
IS VISIBLE ONLY BECAUSE OF THE
Reflection of sunlight.
2. MEDIUM :A substance
through which light propagates or tries is
known as MEDIUM. For example,
Air,water,glass.
etc. On the basis of composition, media (plural of
medium) are classified into following two types:
•HOMOGENEOUS Medium : a medium which possesses the same physcial properties at all it's points, is a homogenous medium. Pure water 💦 and clean sugar is example of Homogenous medium.
•HETEROGENEOUS MEDIUM : When the
the physical properties of the medium are
different at different points, it is a
heterogeneous medium. A thick layer of air in
the atmosphere, which has different densities at
different heights from the earth's surface is an
example of heterogeneous medium.
The basis of the transmission of light, the media
are classified into following three types :
• transparent medium : medium which
permits most of the light to transmit
through it is called a transparent medium.
For example a glass, water, etc.
• translucent medium : the medium which
permits like to be partly transmitted and
partly scattered, is called a translucent
medium. For example ground glass for,
butter paper, frosted glass, etc.
• Opaque medium : the medium which does
not allow light to pass through it is called
an opaque medium. An iron sheet, a thick
cloth, wood, etc. Are some examples of
opaque medium.
3. Ray of light :An extremely
narrow beam of light is called a Ray of
light. Practically, it is the straight line path
along which light travels. In a diagram, it is
represented by a line with an arrow on it
as shown in figure 4.1
 |
You can say that this is a Ray of light
|
the arrowhead indicates the direction in
which the Ray of light travels, i.e., the
direction of propagation of light.
4. Beam of light : A number
of rays combined together form a beam
of light(see figure 4.2).
Pencil of light is a narrow beam of light.
There are following three types of beam of light:
• CONVERGENT BEAM : rays
constituting the beam actually meet at a
point or appear to meet at a particular
point then the beam is called a convergent
beam [see figure 4.3 (a)]
Bus operation between the rays decreases
And the beam becomes narrower as it
travels. Its narrowest point p [see figure
point 4.3 (a)]
• DIVERGENT BEAM: the
rays constituting The beam actually speed
or appear to spread from a point source
the beam is called divergent beam [see
figure point 4.3 b].
Operation between the rays remains
constant throughout us that Bhem travels.
•PARALLEL BEAM : informing the beam are parallel to each other. The beam is said to be a parallel beam. [see fig .4.3(c)]. In between the rays remains constant throughout as the beam travels.
TO be Continued.....
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