The Sun is the largest source of direct energy on Earth. The energy given by the sun is called solar energy.
In 1939, the scientist (Hans Bethe) had propounded a theory about the source of solar energy, according to this theory-
“The source of the Sun’s immense energy is the fusion of lighter nuclei.”
Nuclear Fusion in Sun
The estimated temperature of the outer surface of the Sun is 6900 K and the temperature of its interior is about 2 x 107 K. At this high temperature, the outer electrons are removed from the atoms of all the elements present in the Sun, so they are in the nuclear state.
The velocity of these nuclei is so high that when they collide with each other, their fusion continues automatically and a lot of energy is released.
At high temperature (about 107 K) and pressure, these nuclei of deuterium fuse to form a heavy nucleus of helium. A lot of energy (about 21.6 MeV) is generated in this process.
The reason for this energy generation is that the mass of 2He4 is slightly less than the mass of two 1H2 nuclei, as a result this mass loss is due to the change in energy of mass which is converted into energy according to the equation E = mc2.
Thus this reaction takes place at very high temperature and pressure. The temperature of the center of the Sun is very suitable for this process.
The sun is giving energy at about 4 x 1026 joules/second.
The energy given by sunlight falling on the earth every day is 50,000 times the total energy used by all the countries of the world in a year. Fossil fuels such as coal, petroleum and natural gas have been formed on the earth from the energy of the sun.
Composition of Sunlight
We get solar energy (energy of the sun) in the form of three types of magnetic waves, whose wavelengths are different. These waves are as follows.
- 1 – Ultraviolet waves
- 2 – Visible light waves
- 3 – Infra -red waces
The wavelength of ultraviolet waves present in sunlight is minimum. These rays are invisible, they cannot be seen with the eyes. These waves produce fluorescence in some materials. Their wavelength range 1 x 10-8 to 4 x 10-7 is up to meters. They produce vitamin D in the skin and are more chemically active.
Visible Light Waves
Our eyes can see only a part of the sunlight. which is called visible light. In this light there is a sequence of colors violet, sky, blue, green, yellow, orange, and red.
Among these, violet light has the shortest wavelength and red light has the longest wavelength. Which are respectively expressed by the words VIBGYOR.
Their wavelength ranges from 0.4 microns to 0.70 microns. (1 Microns = 10-6 Meter)
Waves of wavelength greater than that of red light are found in sunlight, which are called infrared waves.
They cannot be seen by the eyes, they can only be experienced by their specific qualities. Their wavelength ranges up to 7.0 x 10-7 to 1 x 10-3 meter. These waves produce the heating effect.
Solar energy Effect
One-third of the sunlight is in the form of infrared light. It increases the temperature of the object coming in its path. They get heat due to the infrared light present in the sunlight.
Infrared light heats the land and water on the Earth’s surface. The upper surface of the Earth’s atmosphere receives about 1.36 joules of energy per square meter per second but all this energy does not reach the Earth, only 47% of it reaches the Earth, while some of the remaining 53% part is in space.
It is reflected and absorbed by the water vapor, ozone, dust and carbon dioxide present in the rest of the atmosphere.
Solar energy is not always available uniformly, the availability of solar energy varies from day to day. Apart from this, this energy is available more in some places of the earth and less at some places.
Solar energy is not available at night. Similarly, even when the sky is cloudy during the day, solar energy is not available in abundance.
In the following table, these waves received from sunlight are expressed in the order of increasing wavelength.
|Ultraviolet waves||Visible light waves||Infra -red waces|
|1 x 10-8 to 4 x 10-7 Meters||4.00 × 10⁻⁷ to 7.00 × 10⁻⁷ Meters||7.0 x 10-7 to 1 x 10-3 meters|
Solar energy Effect
Following are the major uses of the energy obtained from the sun.
1- It is used in solar cooker, solar heater and solar cell.
2 – This gives heat and light to the earth.
3- It provides energy to maintain the cycle of air flow and water circulation on the earth continuously.
4 – With this energy, plants make food by photosynthesis.
5 – With its help, fossil fuels and natural gases are formed on the earth.
Solar energy Effect
When one or more substances interact with each other to form a new product, this type of reaction is called a chemical reaction.
In other words,
“Chemical reaction is the process by which a chemical change results in a change in the molecular organization of the reactants to form new substances completely different from them.”
For example –
The reaction of dilute hydrochloric acid on calcium carbonate forms new products calcium chloride, water and carbon dioxide gas. This reaction can be represented in the following way.
CaCO3 + 2HCl → CaCl2 + H2O + CO2
2- The reaction of sodium and water produces new products sodium hydroxide and hydrogen gas.
2Na + 2H2O → 2NaOH + H2
The first Italian scientist (Enrico Fermi) started the nuclear reaction in the United States of America on December 2, 1942, that is why this day is considered to be the day of entry into the nuclear age.
Such reactions are called nuclear reactions in which a large amount of energy is released along with the change in the nucleus of the atom and new atoms (particles) are formed. This emitted energy is called nuclear energy.
For example, when two protons moving at high velocity collide, a nuclear reaction takes place in which a proton is converted to form a newtron, a positron and a neutrinon and a large amount of energy is released. In this the second proton remains unchanged. This nuclear process is represented by the following nuclear equation:
1H1 + 1H1 → 1H1 + 0n1 + 1e0 + 0v0 + Large Energy
German scientists Hohn and Strassman found in 1939 that when the nucleus of U235 is bombarded with slow-moving neutrons, it splits into nuclei of two dissimilar elements with low atomic numbers, barium and krypton. He called this disintegration nuclear fission.
Hence the process in which a heavy nucleus splits into two smaller dissimilar nuclei and generates immense energy. called nuclear fission.
Nuclear fission is the process of bombardment of slow-moving neutrons on heavy nuclei such as uranium-235. A small amount of mass is lost in the process of nuclear fission, which manifests itself in the form of a lot of energy. In this, the isotopes of smaller elements with mass numbers (atomic mass) from 72 to 162 and atomic numbers between 36 and 58 get a mixture.
Example: When uranium 235 atoms are bombarded with slow neutrons, the heavy nucleus of uranium splits into lighter (medium-weight) atoms barium-139 and Cripton 94 and 3 neutrons are also released. During this a large amount of energy (near about 200 MeV) is also generated. This nuclear fission can be expressed by the following equation –