- We need energy to perform a wide range of activities. Hence, energy is defined as the capacity or ability to do work.
- It is measured in joule, calorie etc.
- According to the law of conservation of energy, energy can neither be created nor be destroyed, but can be transformed from one form to the other.
Sources of energy:
- Energy that we use for various day to day activities is obtained from different sources.
- The natural sources of energy that are used in the same form as they are available are called primary sources of energy, which can be broadly classified into two categories.
- Non-renewable sources of energy
- Those energy sources which cannot be renewed or produced again and again in the nature quickly when exhausted as they have a limited stock in nature.
- Coal, oil and natural gas are such sources, which are commonly known as fossil fuels.
- Renewable sources of energy
- Those energy sources which have existed in nature for billions of years, are being produced continuously and are inexhaustible.
- Energy sources such as sun (solar energy), flowing water (hydro-electricity), wind (wind energy), tides (tidal energy), biogas, geothermal energy etc. are renewable sources of energy.
- Non-renewable sources of energy
Sun (The ultimate source of energy):
- It is the major source of energy for all the living organisms on the earth as it provides us with warmth and light. All other energy sources are the outcome of the solar energy.
- Water evaporates under the influence of the sun and falls in the form of rain.
- Green plants use solar energy to prepare food (glucose) by photosynthesis which is utilized by almost all animals (directly or indirectly) on earth, hence called the ultimate source of energy.
- The sun has inexhaustible amount of hydrogen (72%) and helium (26%) which constitutes about 98% of the mass of the sun.
- Its mass is 2×1030kg, diameter is about 1.4×106 km (about 109 times more than that of the earth) and surface temperature is 57000
- The estimated core temperature of the sun is 15,000,0000C. At such high temperature, no substance can exist in solid or liquid form. Hence, sun is gaseous all through.
- The sun releases about 27×1027 kW energy every second. Every second, one square meter of the earth’s surface receives 1.4 kW power.
- The total solar energy potential in Nepal is estimated to be around 26.6 million MW.
Enormous production of energy in the sun:
- The sun provides all other forms of energy due to a reaction called thermo nuclear fusion reaction.
- In this reaction, two or more light nuclei combine to form a single heavy nucleus at very high temperature and pressure. E. g. formation of helium nucleus from hydrogen nuclei.
- The following is the most possible reaction in the sun among many nuclear reactions.
1H1 + 1H1 —–> 1H2 + 1e0
1H2 + 1H1 —–> 2He3 + ϒ- radiation
2He3 + 2He3 —–> 2He4+ 1H1 + 1H1 + energy
41H1 ——> 2He4 + 21e0 + ϒ- radiation + energy
Simply,
41H1 —–> 2He4 + energy
- In the first step of the above reaction, two protons (1H1) combine to form a deuteron (1H2) and positron (1e0).
- The deuteron thus formed combines with one more proton (1H1) produces a light helium atom (2He3) and gamma (ϒ) radiation.
- Finally, two light helium atoms combine to form a stable form of helium (2He4) along with two protons and energy.
- During this process, a vast amount of energy is produced which is released in the form of heat and light.
- This energy can be calculated by Einstein’s mass energy relation, i. e. E=mc2