Chemical Energy
Energy stored in the bonds of chemical compounds. Propane, C3H8, natural gas, CH4, and phosphorous, P4 react with oxygen O2, and these reactions release energy in the form of heat and light. No doubt, according to the principle of conservation of energy, energy is required to reverse the reactions. Thus, energy stored in chemicals (compounds) and energy released or absorbed in chemical reactions are called chemical energy, which also covers topics such as bond energy, ionization potential, electron affinity, electronegativity, lattice energy, etc.
Heat
Heat energy is energy contained in the vibrational energy of atoms and molecules in a substance that can be transferred by conduction, convection or radiation. Is energy of random molecular motion. The heat that a body possesses depends upon its temperature, its mass, and the kind of material of which it is composed. The unit of heat is the joule.
Solar Energy
Any form of energy radiated by the sun , including light, radio waves, and X rays, although the term usually refers to the visible light of the sun. Solar energy is needed by green plants for the process of photosynthesis , which is the ultimate source of all food. The energy in fossil fuels (e.g., coal and oil) and other organic fuels (e.g., wood) is derived from solar energy.
Difficulties with these fuels have led to the invention of devices that directly convert solar energy into usable forms of energy, such as electricity. Solar batteries, which operate on the principle that light falling on photosensitive substances causes a flow of electricity, play an important part in space satellites and, as they become more efficient, are finding increasing use on the earth.
Thermoelectric generators convert the heat generated by solar energy directly into electricity. Several projects have produced electricity on a large scale by using the solar energy available in desert areas. In one system, large numbers of solar batteries generate electricity for Coconut Island, off the coast of Australia. In another, oil flows through pipes that are set in reflecting parabolic troughs that can trap the heat from sunlight falling on them.
The heat from the oil is then converted into electricity. Heat from the sun is used in air-drying a variety of materials and in producing salt by the evaporation of seawater. Solar heating systems can supply heat and hot water for domestic use; heat collected in special plates on the roof of a house is stored in rocks or water held in a large container. Such systems, however, usually require a conventional heater to supplement them. Solar stoves, which focus the sun's heat directly, are employed in regions where there is much perennial sunlight.
Nuclear Energy
The energy stored in the nucleus of an atom and released through fission, fusion, or radioactivity. In these processes a small amount of mass is converted to energy according to the relationship E = mc2, where E is energy, m is mass, and c is the speed of light. The most pressing problems concerning nuclear energy are the possibility of an accident at a nuclear reactor or fuel plant, such as those which occurred at Three Mile Island (1979), Chernobyl (1986), and Takaimura, Japan (1999), and the potential threat to the continued existence of the human race posed by nuclear weapons.
Mechanical Energy
Sum of a system's kinetic energy and potential energy. Sum of a system's kinetic energy (KE) and potential energy (PE). Mechanical energy is constant in a system that experiences no dissipative forces such as friction or air resistance. For example, a swinging pendulum that experiences only gravitation has greatest KE and least PE at the lowest point on the path of its swing, where its speed is greatest and its height least. It has least KE and greatest PE at the extremities of its swing, where its speed is zero and its height is greatest. As it moves, energy is continuously passing back and forth between the two forms. Neglecting friction and air resistance, the pendulum's mechanical energy is constant.
Electrical Energy
Energy dissipated in an electrical or electronic circuit or device per unit of time. The electrical energy supplied by a current to an appliance enables it to do work or provide some other form of energy such as light or heat. Electric power is usually measured in Watts , kilowatts (1,000 watts), and megawatts (1,000,000 watts). The amount of electrical energy used by an appliance is found by multiplying its consumed power by the length of time of operation. The units of electrical energy are usually watt-seconds (joules), watt-hours, or kilowatt-hours. For commercial purposes the kilowatt-hour is the unit of choice.
