The Sun and Nuclear Fusion
The Sun is the greatest source of energy on the Earth. We would not have been
alive if there is no Sun around us, to give us warmth. The Earth would have
been very cold frozen place.
It’s the sunlight that makes it fit for organism, by giving warmth. The
most basic source of food on Earth- plants make their food in the presence of
sunlight. It powers the flow of find and water cycles on the Earth’s surface and
sustains all life.
Mass of the Sun is about 1029 tonnes. It has been estimated that the sun
has been burning for the last seven to eight billion years. The Sun contains in
its core hydrogen nuclei moving at very great speeds. Whenever these nuclei
fuse to form a nucleus of a heavier element a large amount of energy is
liberated. It is this energy that we receive when the Earth faces the Sun.
What Sunlight is Composed of ?
The sunlight is composed of lights of wavelengths ranging from ultraviolet and the visible to the hot light of infrared. The Sun emits lights of
different wavelengths. Each wavelength gives us different sensation of colour.
If sunlight is allowed to pass through a prism each of these wavelengths is
refracted by a different amount. The result is a beautiful band of the colours of
the rainbow. Violet has the shortest wavelength (0.4 microns) and red has the
longest (0.7 microns). The wavelength of green light (0.53 microns) is midway
between that of violet and red. In fact, Plants which prepare their food by
photosynthesis mainly absorb the violet and red lights. The remaining
wavelengths of light are just reflected back.
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Light whose wavelength is shorter than that of violet is called ultraviolet light. Light whose wavelength is longer than that of red light is called
infra-red light. One-third of the light from the sun is infra-red. Infra-red can
heat up an object in its path. The heat we feel in sunlight is due to the presence
of infrared wavelengths in it. Infra-red light from the Sun heats up the land and
the water on the surface of the Earth. Not all energy from the Sun reaches the
surface of the Earth. Some of the light energy is reflected back in to space,
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some is absorbed by the water vapour, ozone, dust and carbon dioxide present
in the atmosphere. In fact only, 47% of the energy strikes the earth’s
atmosphere reaches the earth’s surface and is absorbed.
What is the Source of Sun’s Energy – the Nucleus
The atom consists of a positively charge heavy nucleus and negatively
charge electrons revolving around the nucleus. The atoms of an element can
have different number of neutrons in their nucleus, even if they had the same
number of protons in their nucleus. For example – the Uranium atom has 92
protons in the nucleus and 92 electrons revolving around it. However, not all
uranium atoms have the same number of neutrons in their nucleus. Some
uranium atoms have 146 neutrons while others have 143 neutrons. These two
forms of uranium are called the isotopes of uranium. The number of protons
and neutrons is called the Mass Number of the atom. The uranium atom with
146 neutrons is designated as U-238(238=92+146) while the uranium atom
with 143 neutrons is designated as U-235.
When two particles like two fast moving protons inside the nucleus of an
atom collide with one another, the colliding proton changes into a neutron and
two new particles are produced. One of these is a positively charged particle of
the same mass as an electron and is called positron. The other is a massless
neutral particle called neutrino. Also, a lot of energy in the form of different
wavelengths is released. These type of nuclear reactions occur in the interior of
the sun which liberates so much energy. Nuclei of deuterium which is the
heavier isotope of hydrogen, collide in the sun’s interior to produce helium.
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The energy liberated in this reaction fires the sun, which in turn emits light of
different wavelengths. The reaction in which hydrogen in the sun is converted
into helium accompanied with release of energy is called a Fusion
reaction. For fusion to occur, the nuclei have to collide at very high speeds.
Such speeds are only possible when the temperature is very high. One gram of
hydrogen in the sun releases about 62 x 109 Joule of Energy.
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