1. Nature of light
Light is weightless,
immaterial and transverse. Light generated by incandescence and luminescence. Incandescence
is the emission of light from hot and luminescence is the emission of light
when excited electrons fall to lower energy level.
The speed of light is
constant in vacuum and speed of light through medium is slower than vacuum. It
depends on medium which it travel or interact.
2. Properties of light
2.1
Radiation
The sun emits heat and
light. These forms constitute only small portion of energy of the total energy
that radiates from the sun. This energy called as radiation or electromagnetic
radiation. All types of radiation travel in a speed of light (x-rays, radio
waves, or heat waves). Electromagnetic radiation comes in various sizes or
wavelengths. Earth gets sun radiation in the form of short wave length.
Radiation often
identified when the rays interact with an object. When it is easy to show that
will call visible light. It appears “white” in color. White light is
corresponding to various colors and each color represent various wave length
and over 95% are between 0.1 and 2.5 micrometers and much of this energy
concentrated in the visible and near-visible parts of the electromagnetic
spectrum.
2.3 Reflection
Light travel through vacuum
of space in a straight line. Rays enter the surface and bounce back from the
surface is to be called reflection. When the rays bounce back from the surface
it reflects the surface in same angle. This principle is called as law of
reflection.
Angle of incidence =
angle of reflection
Incoming rays =
Outgoing ray
This is not perfectly suited
for all objects. It depends on interfere particles and wavelength of the light.
When light rays reach the rough surface the image appear as multiple images and
travel in various directions.
2.4 Refraction
When light travel
through transparent material it’s not bounce back from material. It transmitted
through that material to another medium called refraction. For example when the
light passes through water it get bending in the opposite direction. The amount
of refraction in air is small and in water is much larger.
We can explain this
illusion through sun setting. When the sun near the horizon we can see the sun
few minutes after it has set below the horizon. Solar radiation takes eight
minutes to reach the earth. Therefore we can see only the eight minutes earlier
of the suns apparent located position. This illusion is cause by the result of
bending of solar radiation.
Usually air density
increases in earthwards. This gradual density changes are equal for gradual
slowing and bending of light.
3. Rainbows
This optical phenomenon
can see when the observer is situated with the sun on one side and rain shower
occur in opposite side. The rainbow outer part start with red color and it
gradually blends to orange, yellow, green, blue and violet. In this situation
observer can see the view of dimmer secondary rainbow near the primary one. The
second bow will appear 80 above the primary bow and it in reverse
colors order that red in inner part and violet in outer part of the rainbow.
The sunlight and water
droplets are needed for the formation of rainbow. When the light passes through
water it speed slowed and gets refracted in different angle and each color of
light travel at different velocity in water.
This phenomenon was
demonstrated by Sir Isaac Newton through using a prism. Newton noted when the
light passes through prism it refracted twice. Once it enters into the prism
and after it exists. In this occasion water droplets act as a prism and
disperse the sunlight. The rainbow appears in curved shape because rays reach
the observer in the angle of 400 and 420 from the
sunlight path.
3. Halos, Sun dogs and
Solar pillars
Halos:
This optical phenomenon
can see any observer and it often appear morning and late afternoon when the
sun is near the horizon. It also generated by dispersion of sunlight. These
halos are mostly associated with cirrus clouds.
Four types of ice crystals
that compose cirrus clouds are contribute to the formation if halos: plates,
columns, capped columns and bullets. Sunlight strikes these crystals in all
angles and light get scattered and disperse equally in all directions.
Halos are commonly
whitish in color. Ice crystals are dispersing the light as a rain droplets or
prism. The color produced by the light reddish band is in inner portion of the
ring and other colors tend to washout each other and leave the red surrounded
by whitish ring.
Most spectacular effect
that associated with halos is sun dogs or perihelia and sun pillar. Sun dogs
forms under the same condition. This phenomenon is happen when the ice crystals
are allowed to descend slowly. Sun pillar are most often viewed near sunset or
sunrise and appear in vertical from the sun.
References:
1. Frederick K. Lutgens, Edward J. Tarbuck, Dennis Tasa (2010); The Atmosphere : An introduction to Meterology; Pearson Education, Inc. USA.
2. http://physics.info/light
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