Electric Circuits
What are Electric Circuits?
An electric circuit is the course along which an electric current flows. Electrons carrying negative charge can be moved around a circuit by electrostatic forces. A circuit usually consists of a conductive material, such as a metal, where the electrons are held very loosely to their atoms, thus making movement possible. The strength of the electrostatic force is the voltage, and is measured in volts. The resulting movement of electric charge is called an electric current, as is measured in amps. The higher the voltage, the greater the current will be. But the current also depends on the thickness, length, temperature, and nature of the material that conducts it. The resistance of a material is the extent to which it opposes the flow of electric current, and is measured in ohms. Good conductors have a low resistance, which means that a small voltage will produce a large current. In batteries, the dissolving of a metal electrode causes the freeing of electrons, resulting in their movement to another electrode and the formation of a current.
Mathematics
Electricians and engineers use several mathematical formulas to calculate the current and voltage in each part of a circuit. The most important of these formulas are Ohm's law and Kirchhoff's laws. They were discovered by two German physicists, Georg S. Ohm and Gustav R. Kirchhoff.
Georg Simon Ohm
His Life
The German physicist Georg Simon Ohm, b. Mar. 16, 1789, d. July 6, 1854, for whom the unit of electrical resistance, the ohm, was named, determined (1826) Ohm's law--the relationship between the flow of current, the voltage, and the resistance in a closed circuit. Ohm's scientific contemporaries were slow to recognize his achievement, failing to realize how closely his conclusions were derived from careful experimental work and especially how his discovery ordered vast quantities of existing experimental data. For most of his life Ohm held only indifferent, poorly paid teaching jobs, but in 1852 he was given the chair of physics at the University of Munich.
Ohm's Law
Gustav Robert KirchhoffOhm's Law states that a thin wire has resistance to the flow of current . The longer and thinner the wire, the higher the resistance. An object's resistance can be worked out by dividing the voltage by the current.
Ohm's law relates the voltage and current in a circuit to the resistance of the circuit. Resistance opposes the flow of electricity and consumes power from the circuit by changing electric energy into heat. Electricians measure resistance in units called ohms. Ohm's law is expressed in the equation V = IR. This law states that the voltage (V) equals the current (I) multiplied by the resistance (R), through which the current flows.
His Life
Gustav Robert Kirchhoff(1824-1887), was a German physicist who made important discoveries about elements, electricity, and radiation. Kirchhoff was born in Koningsberg, now Kaliningrad, Russia. In 1847, he graduated from the University of Koningsberg. Kirchhoff taught at the University of Heidelberg from 1854 to 1875.His most famous for his study of light broken up into its individual colors. Kirchhoff devised laws of electricity and radiation, now called Kirchhoff's laws. The laws of electricity provide formulas describing the flow of electrical current. The law of radiation states that a substance's capacity to emit light equals its ability to absorb light at the same temperature.
First Law
Kirchhoff's first law states that the sum of the currents entering any point in a circuit equals the sum of the currents leaving that point. This law is based on the fact that an electric charge cannot accumulate at any point in a closed circuit.
Second Law
Kirchhoff's second law states that the sum of the changes in voltage around any circuit is zero. In other words, the voltage increases through the sources by the same amount that it decreases through the output devices.