Electric circuits

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Chapter 0 - INTRODUCTION - Some notes about History

Before electricity became available over 100 years ago, houses were lit with kerosene lamps, food was cooled in iceboxes, and rooms were warmed by wood-burning or coal-burning stoves.
Many scientists and inventors have worked to decipher the principles of electricity since the 1600s. Some notable accomplishments were made by BenjaminFranklin, Thomas Edison, and Nikola Tesla.
Benjamin Franklin demonstrated that lightning is electricity. Thomas Edison invented the first long-lasting incandescent light bulb.
Prior to 1879, direct current (DC) electricity had been used in arc lights for outdoor lighting. In the late 1800s, Nikola Tesla pioneered the generation, transmission, and use of alternating current (AC) electricity, whichreduced the cost of transmitting electricity over long distances. Tesla's inventions used electricity to bring indoor lighting to our homes and to power industrial machines.
Despite its great importance in our daily lives, few of us probably stop to think what life would be like without electricity. Like air and water, we tend to take electricity for granted. But we use electricity to do many jobs forus every day — from lighting, heating, and cooling our homes to powering our televisions and computers.
Electrical energy is not generally referred to as electrical energy for the layperson, and is most commonly known as electricity. Electrical energy is the scientific form of electricity, and refers to theflow of power or the flow of charges along a conductor to create energy. Electrical energy is known to be a secondary source of energy, which means that we obtain electrical energy through the conversion of other forms of energy. These other forms of energy are known as the primary sources of energy and can be used from coal, nuclear energy, natural gas, or oil.

The primary sources from whichwe create electrical energy can be either non-renewable forms of energy or renewable forms of energy. Electrical energy however, is neither non-renewable or renewable.

Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.

Electric energy is transmitted with overhead lines on pylons like these shown in the picture fromBrisbane, Australia. For underground transmission, high voltage cables are used.

When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work. Devices convert electrical energy into many useful forms, such as heat (electric heaters), light (light bulbs), motion (electric motors), sound (loudspeaker), information technological processes (computers), or evenchemical changes.

Electricity can be produced mechanically by generation, or chemically, or by direct conversion from light in photovoltaic cells, also it can be stored chemically in batteries.


The atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomicnucleus contains a mix of positively charged protons and electrically neutral neutron.

The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive charge (electron deficiency) or negativecharge (electron excess) and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.

An electron is one of the most important types of subatomic particles. Electrons combine with proton and (usually) neutrons to make atoms....
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