1786 Alessandro Giuseppe Antonio Volta - Italy


Invented the Battery an electrochemical cell made of Zinc and Copper plates in a sulfuric acid solution.

A chemical reaction between the Sulfuric acid, Zinc and Copper creates an electric pressure which is defined in units called Volts. Batteries are devices that provide Direct Current DC electricity. If a conductor is connected from the Positive + side of a battery to the Negative - side of a battery; electrons will flow from the Negative - side to the Positive + side creating an electric current.


1806 André-Marie Ampère - France


Primarily discovered the relationship between electricity and magnetism, Electromagnetism.

Electrical current is defined in units called Amps. When an electric current flows through a conductor a magnetic field is created around the conductor. If a magnetic field, moves around a conductor an electrical current (electron flow) is created. Electric fields exist around electrons and electrons in motion produce magnetic fields. The combination of an electric field and magnetic field,  electromagnetic field, can exist without electrons and will travel through space at the speed of light. Radio waves and Light are examples of electromagnetic radiation.



1829 Michael Faraday  - England

Contributed greatly to the discoveries of Electromagnetism and Electrochemistry. Improved on discoveries by Hans Christian Ørsted to invent the first working electric motor. Magnetic fields interact between the Rotor and Stator in electric motors causing the Rotor to turn.  An electric motor becomes a generator when the rotor is turned by an external force.

The unit for electrical capacitance is the Farad.  Leyden Jars invented in 1700 were early versions of capacitors.  Because of the electrical law of attraction and repulsion capacitors can store an electric charge. Capacitors consist of two conducting plates separated by an insulator. When electrons accumulate on one plate then electrons are repelled from the other plate causing a stored charge.  Capacitors block DC but will pass AC.

1853 James Prescott Joule - England


Discovered the relationship of heat, mechanical work and energy and the relationship between electric current, resistance and heat dissipation.  The unit of energy is called the Joule. The work required to move an electric charge of one Coulomb through one volt is one Joule. The unit for electric charge is the Coulomb and is named after Charles-Augustin de Coulomb.

1821 Georg Simon Ohm - Germany


Discovered the relationship between the Voltage applied across a Conductor and the resultant Electric Current in Amps; this is now known as Ohm’s law.  The unit of resistance is the Ohm. Resistors, are devices that hinder the flow of electric current. Resistors, can be made of carbon or resistive wire. Most resistors have color bands that are used to tell the resistance in Ohms;  this is known as the resistor color code.



1837 Joseph Henry - United States


Discovered the phenomenon of self inductance and mutual inductance. The unit of inductance is the Henry. Inductors are coiled wires that have a magnetic field around them when an electric current flows through them.  Inductors are used in relays, telegraphs, and transformers. In a relay an induced magnetic field closes a switch connection. The same is true for a telegraph. a transformer changes AC voltages. Inductors impede AC but pass DC.

1786 James Watt - Scotland


Perfected the steam engine. The unit of electrical power is called the Watt. Steam engines are commonly used to drive Generators DC and Alternators AC to produce electrical power.

1880 to1930 Léon Thévenin - Gustav Kirchhoff - Edward Norton

Methods to analyze circuits

Léon Thévenin determined that any circuit combination of voltage sources, current sources and resistors with two terminals can be simplified to a circuit with a voltage source with a series resistor.


Edward Norton determined that any circuit combination of voltage sources, current sources and resistors with two terminals can be simplified to a circuit with a voltage source with a parallel resistor.


Gustav Kirchhoff determined that the current entering a point was equivalent to the current leaving the same point and that the sum of the voltage drops around any closed loop equals the applied voltage.

1889 Thomas Alva Edison  - United States


Invented the electric Light Bulb, Phonograph, Carbon Microphone, Electric Chair and developed DC electric power distribution systems and 1089 other patented inventions.


A light bulb is an evacuated glass envelope with a conductor (filament) inside that is heated to a point where it glows bright white when an electric current is passed through it. Lewis Howard Latimer developed the carbon filament for Edison.


A phonograph takes compressions and rarifications of air molecules (Sound) and scratches a moving groove on a rotating disk or drum. Later, when a stylus connected to a speaker diaphragm is influenced by the recording on the groove of a turned drum or disk, sound is reproduced.


A carbon microphone is a disk containing carbon powder. When sound hits the diaphragm side of the disk the carbon powder is compressed or rarified. An electric current passing through the carbon powder is changed according to the sound making an audio signal.

















1832 Samuel Finley Breese Morse - United States


Principal inventor of the single wire telegraph and Morse code. William Cooke, Charles Wheatstone, Wilhelm Weber, David Alter, Alfred Vail and Carl Gauß were also involved with the invention of the telegraph. 

When the send key is pressed batteries A and B cause current to flow from earth ground Boston to Earth ground New York causing magnetic fields to develop in coils C and D. When coils C and D have magnetic fields they close contacts E and F. Batteries J and I cause a current flow through sounders H and G making a loud click. Pressing the send key in New York causes a loud click in Boston.

1900 Nikola Tesla - Serbia - United States


Discovered Alternating Current AC, Multi-phase power systems and developed the AC generator alternator, AC motor and wireless energy transfer. The unit of magnetic flux density is the Tesla.  Tesla worked with Thomas Alva Edison and was a good friend of Mark Twain. Tesla’s work formed the basis of modern power generation and distribution systems.

1884 Alexander Graham Bell - Scotland - Canada - United States


Invented the first practical telephone.  A telephone is a device that transmits sound over wire bidirectionally.


Batteries E and F establish a current flow through speakers B and D and carbon microphones A and C. When compressions and rarifications of air molecules (Sound) move the diaphragm in carbon microphone A the carbon has a change in resistance proportional to the sound hitting the microphone. This causes undulating  current flow through the system. The undulating current passing through speaker B causes the speaker diaphragm to move creating an equivalent sound to that heard by microphone A. The same process is true in the reverse direction. Modern microphones can be Carbon, Dynamic (magnetic) or capacitive. But in any case, a microphone turns sound into an electrical signal. Conversely, a speaker turns an electrical signal into sound.


1917 Lee De Forest - United States

Invented the triode tube. Edison and Sir John Ambrose Fleming also contributed to the development of the electron tube (valve). Edison, discovered that electrons would boil off the filament in a light bulb. Fleming inserted another metal plate in a light bulb (making a diode tube) and found that it would only allow current to flow from the filament (Cathode) to the plate (Anode) turning alternating current  into direct current. De Forest inserted a wire mesh between the cathode and anode making a triode tube. Triode tubes (Audions) have the ability to amplify electronic signals.

A power supply turns AC into DC. The transformer T1 is connected to the wall AC using plug P1. The transformer then steps down the voltage to provide power for the heater in the tube.  Another winding on the transformer steps up the voltage so the tube can operate. The tube only allows  current to flow from cathode to anode turning AC into DC. Capacitor C1 filters the ripple out making pure DC.


Oscilloscope waveforms are shown in this drawing. The Oscilloscope was invented by Allen Balcom DuMont to allow viewing of electronic waveforms.



Memory Point -  Beaten British Rage Over Your Great Big Victorious George Washington.

Memory Point - Cats are Black and Ants are Red = Cathodes are negative and Anodes are positive.

Audion Amplifier - The input voltage can be any kind of alternating current signal such as an audio signal from a microphone.

The signal flows through resistor R3 (Volume Control) which determines the amount (Amplitude) of signal fed to the grid of the triode tube.

Capacitor C1 passes the AC signal but blocks DC so a proper DC bias can be maintained on the grid.

Resistors R1 and R2 divide the voltage from battery B1 to ground to produce the correct DC bias on the grid of the triode tube. A Bias is a DC voltage that establishes the correct point of tube conductivity to allow the input signal to control current flow from cathode to anode of the tube.

The heater is like a filament in a light bulb the heated cathode can have electrons flow from it. Sometimes, this is called boiling electrons from the cathode. In some tubes the heater is the cathode. The anode has a high positive DC voltage on it from battery B1 the electrons from the cathode are attracted to the anode causing a current flow. The signal on the grid controls (modulates) the flow from cathode to the anode. Amplification is caused when a small signal controls a large current flow that creates a large signal.

Transformer T1 decouples DC and matches impedance  to allow the loud speaker to turn the signal into sound.

If a connection from the output back to the input of the amplifier is created the signal will feedback turning the amplifier into an oscillator

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