Since electric current is invisible and the processes at play in electronics are often difficult to understand in an intuitive way, it is common to teach electronics using analogies to more common sense objects and processes. Probably the most widely used analogy is made to a hydraulic system of water in pipes. The "electron fluid" in a metal conductor has many similarities to such a system, and the various electronic components have similar hydraulic equivalents. In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ... Two digital voltmeters The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. ... Look up Common sense in Wiktionary, the free dictionary For the American independence advocacy pamphlet by Thomas Paine, see Common Sense (pamphlet) For the American hip-hop artist, see Common One meaning of the term common sense (or as an adjective, commonsense) on a strict construction of the term, is... Hydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. ... Electronics is the study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. ...

Electricity (as well as heat) was originally understood to be a kind of fluid. This hydraulic analogy is still of some use in teaching, not only for the fact that the names of the quantities are often struck by analogy.

The water analogy is very useful in describing some aspects of electricity, but it breaks down for others.

Basic ideas

There are two basic paradigms:

• Version with pressure induced by gravity. Large tanks of water that are held up high, and the potential energy of the water head is the pressure source. This is reminiscent of electrical diagrams with an up arrow pointing to +V, grounded pins that otherwise are not shown connecting to anything, and so on.
• Completely enclosed version with pumps providing pressure only; no gravity. This is reminiscent of a circuit diagram with a voltage source shown and the wires actually completing a circuit.

In fluid dynamics, head refers to the constant right hand side in the incompressible steady version of Bernoullis equation. ...

Component equivalents

Wires 

All pipes are completely full of water, and none ever has an open end. If a pipe were to go somewhere without reconnecting to the circuit, it would have to have a cap on the end. This is because the wall of the pipe is like an insulator, and a wire just sticking out into insulating space/air is like a completely pipe-surrounded rod of water.

Potential 

Equivalent to pressure.

Voltage 

Also called potential difference. A relative difference in pressure between two points

Current 

The amount of charge (i.e. electrons, electron holes or ions) passing through a cross section of conductor per given time, much like a hydraulic mass flow rate.

Ideal voltage source 

A pump with a pressure meter on both sides. It varies the speed of the pump to keep the difference in pressure constant.

Ideal current source 

Also a pump, but with a current meter (little paddle wheel). The pump changes speed to maintain a constant speed of the little paddle wheel.

Resistor 

A pipe with a small width. "So what makes this different from a regular-width pipe?" Nothing. All pipes have some resistance, just like all wires have some resistance.

A capacitor driven by an AC source through a diode.

Diode 

One-way valve or check valve. If it has a rubber flap it can be blown out permanently by too much reverse bias, which is similar to the real thing.

Capacitor 

Big spherical tanks with a sheet of thick rubber separating the two halves.

Inductor 

All flowing water has inertia, which has similar effects to inductance. A large, heavy, frictionless paddle wheel is like a dedicated inductor. As you try to increase a DC current, you encounter resistance as you speed up the paddle wheel, but after it is going, you can send a current at the same speed as the paddle wheel with no effort. If you try to put AC through it, the wheel will present a great resistance, as its inertia prevents you from moving it back and forth. Any real paddle wheel will have some friction associated with it, just as any real inductor has some resistance. The DC to DC converter uses inductance to change voltage in the way that a Hydraulic ram uses inertia to change pressure.

Transistor 

A device similar to an EGR valve, where a diaphragm controlled by a low-current signal (either constant current - BJT, or constant pressure - FET) moves a plunger which allows a larger current to flow through another section of pipe, like a globe valve.

CMOS 

A combination of two MOSFET transistors. As the input pressure changes, the pistons allow the output to connect to either zero or positive pressure.

A wire is a single, usually cylindrical, elongated strand of drawn metal. ... It has been suggested that this article or section be merged with Scalar potential. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ... This article may be too technical for most readers to understand. ... In electricity, current refers to electric current, which is the flow of electric charge. ... Properties The electron is a fundamental subatomic particle which carries a negative electric charge. ... In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. ... An ion is an atom or group of atoms with a net electric charge. ... Cross section may refer to the following In geometry, Cross section is the intersection of a 3-dimensional body with a plane. ... Mass flow rate is the movement of mass per time. ... An ideal voltage source, V, driving a resistor, R, and creating a current I A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force. ... An ideal current source, I, driving a resistor, R, and creating a voltage V A current source is an electrical or electronic device that delivers or absorbs electric current. ... A paddle steamer, paddleboat, or paddlewheeler is a ship driven by one or more paddle wheels driven by a steam engine. ... Resistor symbols A resistor is a two-terminal electrical or electronic component that resists the flow of current, producing a voltage drop between its terminals in accordance with Ohms law. ... Image File history File links Water_cap_and_diode. ... Image File history File links Water_cap_and_diode. ... Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... this siamese clappered inlet allows one or two inputs into a deluge gun A check valve is a mechanical device, a valve, that normally allows fluid to flow through it in only one direction. ... A p-n junction is formed by combining N-type and P-type semiconductors together in very close contact. ... A capacitor is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. ... An inductor is a passive electrical device that creates a magnetic field when a current (AC or DC) is passed through it. ... In psychology, social inertia describes a persons resistance to change. ... In electrical engineering, a DC to DC converter is a circuit which converts DC power from one voltage to another. ... A hydraulic ram is a water-powered cyclic pump. ... Assorted component transistors The transistor is a solid state semiconductor device which can be used for amplification, switching, voltage stabilization, signal modulation and many other functions. ... Exhaust gas recirculation (EGR) was an early and primitive automobile emissions-control device that was used from the late 1960s through the early 1980s. ... The schematic symbols for pnp- and npn-type BJTs. ... This article has been identified as possibly containing errors. ... Globe valves are named for their spherical body shape. ... Static CMOS Inverter CMOS (pronounced see-moss), which stands for complementary metal-oxide-semiconductor, is a major class of integrated circuits. ... The MOSFET, or Metal Oxide Semiconductor Field-Effect Transistor, is by far the most common field-effect transistor in both digital and analog circuits (The Metal in the name is an anachronism from early chips where gates were metal; modern chips use polysilicon gates, but are still called MOSFETs). ...

Principle equivalents

EM wave speed (velocity of propagation) 

Speed of sound in water. When a light switch is flipped, the electric wave travels very quickly through the wires.

Charge flow speed  

Particle speed of water. The moving charges themselves move rather slowly.

DC 

Constant flow of water in a circuit

Higher-frequency AC 

Sound being transmitted through the water

Inductive spark 

Used in induction coils, similar to water hammer

Velocity of Propagation (VoP) is a parameter that characterizes the speed at which an electrical or radio signal passes through a medium. ... The speed of sound c (from Latin celeritas, velocity) varies depending on the medium through which the sound waves pass. ... DC may stand for: Augustin Pyrame de Candolle in binomial nomenclature Axiom of dependent choice in set theory (mathematics) Da capo, a musical term DC Comics, a comic book publisher whose name is derived from one of its flagship titles, Detective Comics DC Shoes, a skateboarding apparel manafacturer Democrazia Cristiana... city lights viewed in a motion blurred exposure. ... A schematic representation of hearing. ... An induction coil (archaically known as a Ruhmkorff coil) is a type of disruptive discharge coil. ... Water hammer (or, more generally, fluid hammer) is a pressure surge or wave caused by the kinetic energy of a fluid in motion when it is forced to stop or change direction suddenly. ...

Equation examples

Some examples of equivalent electrical and hydraulic equations:

Hydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. ... The article on electrical energy is located elsewhere. ... This article is about the atmospheric phenomenon. ... Quantity is a generic term used when referring to the measurement (count, amount) of a scalar, vector, number of items or to some other way of denominating the value of a collection or group of items. ... Volume, also called capacity, is a quantification of how much space an object occupies. ... Charge is a word with many different meanings. ... A red-hot iron rod cooling after being worked by a blacksmith. ... It has been suggested that this article or section be merged with Scalar potential. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ... Electric potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... A current is the rate of fluid flow, especially water or air. ... In electricity, current refers to electric current, which is the flow of electric charge. ... This article is about velocity in physics. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ... The Poiseuilles law (or the Hagen-Poiseuille law also named after Gotthilf Heinrich Ludwig Hagen (1797-1884) for his experiments in 1839) is the physical law concerning the voluminal laminar stationary flow ΦV of incompressible uniform viscous liquid (so called Newtonian fluid) through a cylindrical tube with the constant... Ohms law, named after its discoverer Georg Ohm [1], states that the potential difference or voltage drop (U or V) between the ends of a conductor and the current (I) flowing through the conductor are proportional at a given temperature: The equation contains the proportionality constant R, which is... Heat flow along perfectly insulated wire Heat conduction is the transmission of heat across matter. ...

External links

Good analogy

• Hyperphysics
• Hyperphysics 2 - Doesn't have the confusing reservoir.
• Cap charging and discharging
• With animations! - The paddle behaves like a resistor if the paddle itself is massless and has friction, and like an inductor if it is frictionless and has mass. Also has equivalent equations.
• Ohm's law
• Capacitor analogy
• Newsgroup thread with lots of good analogies and a few bad ones

Acceptable analogy

• Understanding Electricity - an analogy with water
• Water analogy to transistors Slightly better version would be something like an EGR valve
• Basic circuit theory
• Measuring electricity
• Plumbing analogy
• Animation