Switch

Electrical switches. Top, left to right: circuit breaker, mercury switch, wafer switch, DIP switch, surface mount switch, reed switch. Bottom, left to right: wall switch (U.S. style), miniature toggle switch, in-line switch, push-button switch, rocker switch, microswitch.

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.^[1][2] The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts are touching and electricity can flow between them, or 'open', meaning the contacts are separated and nonconducting.

A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another workpiece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force, acting as sensors in a process and used to automatically control a system. For example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by another electrical circuit is called a relay. Large switches may be remotely operated by a motor drive mechanism. Some switches are used to isolate electric power from a system, providing a visible point of isolation that can be pad-locked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock.

• 1 In circuit theory
• 2 Contacts
  • 2.1 Contact terminology
  • 2.2 Contact bounce
  • 2.3 Arcs and quenching
  • 2.4 Power switching
  • 2.5 Inductive loads
• 3 Actuator
  • 3.1 Biased switches
  • 3.2 Toggle switch
• 4 Special types
  • 4.1 Mercury tilt switch
  • 4.2 Knife switch
  • 4.3 Footswitch
  • 4.4 Reversing switch
• 5 Light switches
• 6 Electronic switches
• 7 See also
• 8 References
• 9 External links

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Engine

An engine or motor is a machine designed to convert energy into useful mechanical motion.^[1][2]

Motors converting heat energy into motion are usually referred to as engines,^[3] which come in many types. A common type is a heat engine such as an internal combustion engine which typically burns a fuel with air and uses the hot gases for generating power. External combustion engines such as steam engines use heat to generate motion via a separate working fluid.

Another common type of motor is the electric motor. This takes electrical energy and generates mechanical motion via varying electromagnetic fields.

Other motors including pneumatic motors that are driven by compressed air, and motors can be driven by elastic energy, such as springs. Some motors are driven by non combustive chemical reactions. Molecular motors like myosins in muscles generate useful mechanical motion in biological systems by chemical reactions like ATP hydrolysis.

• 1 Terminology
• 2 History of engines
  • 2.1 Antiquity
  • 2.2 Medieval
  • 2.3 Industrial revolution
    • 2.3.1 Horizontally opposed pistons
    • 2.3.2 Advancement
    • 2.3.3 Increasing power
    • 2.3.4 Combustion efficiency
    • 2.3.5 Engine configuration
• 3 Heat engine
  • 3.1 Combustion engine
    • 3.1.1 Internal combustion engine
    • 3.1.2 External combustion engine
    • 3.1.3 Gas turbine
    • 3.1.4 Air-breathing combustion engines
      • 3.1.4.1 Examples
    • 3.1.5 Environmental effects
    • 3.1.6 Air quality
  • 3.2 Non combustive heat engines
• 4 Non thermal chemically powered motor
• 5 Electric motor
• 6 Physically powered motor
  • 6.1 Pneumatic motor
  • 6.2 Hydraulic engine
• 7 Sound levels
• 8 Engine efficiency
• 9 Engines by use
• 10 See also
• 11 References
• 12 External links

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Battery (electricity)

Various cells and batteries (top-left to bottom-right): two AA, one D, one handheld ham radio battery, two 9-volt (PP3), two AAA, one C, one camcorder battery, one cordless phone battery.

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy.^[1] Since the invention of the first battery (or "voltaic pile") in 1800 by Alessandro Volta, batteries have become a common power source for many household and industrial applications. According to a 2005 estimate, the worldwide battery industry generates US$48 billion in sales each year,^[2] with 6% annual growth.^[3]

There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. Batteries come in many sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers.

• 1 History
• 2 Principle of operation
• 3 Categories and types of batteries
  • 3.1 Primary batteries
  • 3.2 Secondary batteries
  • 3.3 Battery cell types
    • 3.3.1 Wet cell
    • 3.3.2 Dry cell
    • 3.3.3 Molten salt
    • 3.3.4 Reserve
  • 3.4 Battery cell performance
• 4 Battery capacity and discharging
  • 4.1 Fastest charging, largest, and lightest batteries
• 5 Battery lifetime
  • 5.1 Life of primary batteries
    • 5.1.1 Battery sizes
  • 5.2 Lifespan of rechargeable batteries
  • 5.3 Extending battery life
  • 5.4 Prolonging life in multiple cells through cell balancing
• 6 Hazards
  • 6.1 Explosion
  • 6.2 Leakage
  • 6.3 Environmental concerns
  • 6.4 Ingestion
• 7 Battery chemistry
  • 7.1 Primary battery chemistries
  • 7.2 Rechargeable battery chemistries
• 8 Homemade cells
• 9 See also
• 10 References
• 11 Further reading
• 12 External links

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Relay

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Automotive-style miniature relay, dust cover is taken off

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

• 1 Basic design and operation
• 2 Types
  • 2.1 Latching relay
  • 2.2 Reed relay
    • 2.2.1 Mercury-wetted relay
  • 2.3 Polarized relay
  • 2.4 Machine tool relay
  • 2.5 Contactor relay
  • 2.6 Solid-state relay
  • 2.7 Solid state contactor relay
  • 2.8 Buchholz relay
  • 2.9 Forced-guided contacts relay
  • 2.10 Overload protection relay
• 3 Pole and throw
• 4 Applications
• 5 Relay application considerations
• 6 Protective relays
• 7 Railway signalling
• 8 See also
• 9 References
• 10 External links

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Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow (as opposed to ionic conductivity) intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 10³ to 10⁻⁸ siemens per centimeter. Semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices. Such devices include transistors, solar cells, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits. Similarly, semiconductor solar photovoltaic panels directly convert light energy into electrical energy. In a metallic conductor, current is carried by the flow of electrons. In semiconductors, current is often schematized as being carried either by the flow of electrons or by the flow of positively charged "holes" in the electron structure of the material. Actually, however, in both cases only electron movements are involved.

Common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of proportions. Such compounds share with better known semiconductors intermediate conductivity and a rapid variation of conductivity with temperature, as well as occasional negative resistance. Such disordered materials lack the rigid crystalline structure of conventional semiconductors such as silicon and are generally used in thin film structures, which are less demanding for as concerns the electronic quality of the material and thus are relatively insensitive to impurities and radiation damage. Organic semiconductors, that is, organic materials with properties resembling conventional semiconductors, are also known.

Silicon is used to create most semiconductors commercially. Dozens of other materials are used, including germanium, gallium arsenide, and silicon carbide. A pure semiconductor is often called an “intrinsic” semiconductor. The electronic properties and the conductivity of a semiconductor can be changed in a controlled manner by adding very small quantities of other elements, called “dopants”, to the intrinsic material. In crystalline silicon typically this is achieved by adding impurities of boron or phosphorus to the melt and then allowing the melt to solidify into the crystal. This process is called "doping".^[1]

• 1 Explaining semiconductor energy bands
• 2 Energy bands and electrical conduction
• 3 Holes: electron absence as a charge carrier
• 4 Energy–momentum dispersion
• 5 Carrier generation and recombination
• 6 Semi-insulators
• 7 Doping
  • 7.1 Dopants
  • 7.2 Carrier concentration
  • 7.3 Effect on band structure
• 8 Preparation of semiconductor materials
• 9 See also
• 10 References
• 11 Further reading
• 12 External links

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Electronics

Surface mount electronic components

Electronics is the branch of science and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits. The nonlinear behaviour of these components and their ability to control electron flows makes amplification of weak signals possible, and is usually applied to information and signal processing. Electronics is distinct from electrical and electro-mechanical science and technology, which deals with the generation, distribution, switching, storage and conversion of electrical energy to and from other energy forms using wires, motors, generators, batteries, switches, relays, transformers, resistors and other passive components. This distinction started around 1906 with the invention by Lee De Forest of the triode, which made electrical amplification of weak radio signals and audio signals possible with a non-mechanical device. Until 1950 this field was called "radio technology" because its principal application was the design and theory of radio transmitters, receivers and vacuum tubes.

Today, most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solid state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This article focuses on engineering aspects of electronics.

• 1 Electronic devices and components
• 2 Types of circuits
  • 2.1 Analog circuits
  • 2.2 Digital circuits
• 3 Heat dissipation and thermal management
• 4 Noise
• 5 Electronics theory
• 6 Electronics lab
• 7 Computer aided design (CAD)
• 8 Construction methods
• 9 See also
• 10 References
• 11 Further reading
• 12 External links

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Transistor

Assorted discrete transistors. Packages in order from top to bottom: TO-3, TO-126, TO-92, SOT-23

A transistor is a semiconductor device used to amplify and switch electronic signals. It is made of a solid piece of semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things.

• 1 History
• 2 Importance
  • 2.1 Usage
• 3 Simplified operation
  • 3.1 Transistor as a switch
  • 3.2 Transistor as an amplifier
• 4 Comparison with vacuum tubes
  • 4.1 Advantages
  • 4.2 Limitations
• 5 Types
  • 5.1 Bipolar junction transistor
  • 5.2 Field-effect transistor
  • 5.3 Other transistor types
  • 5.4 Part numbers
    • 5.4.1 Other schemes
    • 5.4.2 Naming problems
• 6 Construction
  • 6.1 Semiconductor material
  • 6.2 Packaging
• 7 See also
• 8 References
• 9 Further reading
• 10 External links
  • 10.1 Datasheets
  • 10.2 Patents

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Electronic band structure

Electronic structure methods   Tight binding Nearly-free electron model Hartree–Fock method Modern valence bond Generalized valence bond Møller–Plesset perturbation theory Configuration interaction Coupled cluster Multi-configurational self-consistent field Density functional theory Quantum chemistry composite methods Quantum Monte Carlo k·p perturbation theory Muffin-tin approximation LCAO method   Book · Category This box: view · talk · edit

In solid-state physics, the electronic band structure (or simply band structure) of a solid describes those ranges of energy an electron is "forbidden" or "allowed" to have. Band structure derives from the diffraction of the quantum mechanical electron waves in a periodic crystal lattice with a specific crystal system and Bravais lattice. The band structure of a material determines several characteristics, in particular the material's electronic and optical properties.

• 1 Why bands occur in materials
• 2 Basic concepts
  • 2.1 Symmetry
  • 2.2 Band structures in different types of solids
  • 2.3 Density of states
  • 2.4 Filling of bands
• 3 Theory of band structures in crystals
  • 3.1 Nearly free electron approximation
  • 3.2 Tight-binding model
  • 3.3 KKR model
  • 3.4 Order-N spectral methods
  • 3.5 Density-functional theory
  • 3.6 Green's function methods and the ab initio GW approximation
  • 3.7 Mott insulators
  • 3.8 Augmented plane waves
  • 3.9 Others
• 4 References
• 5 Bibliography
• 6 Further reading
• 7 See also

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Electron

Electron
Experiments with a Crookes tube first demonstrated the particle nature of electrons. In this illustration, the profile of the cross-shaped target is projected against the tube face at right by a beam of electrons.[1]
Composition:	Elementary particle[2]
Particle statistics:	Fermionic
Group:	Lepton
Generation:	First
Interaction:	Gravity, Electromagnetic, Weak
Symbol(s):	e− , β−
Antiparticle:	Positron (also called antielectron)
Theorized:	Richard Laming (1838–1851),[3] G. Johnstone Stoney (1874) and others.[4][5]
Discovered:	J. J. Thomson (1897)[6]
Mass:	9.10938215(45)×10−31  kg[7] 5.4857990943(23)×10−4  u[7] [1,822.88850204(77)]−1 u[note 1] 0.510998910(13) MeV/c2[7]
Electric charge:	−1 e[note 2] −1.602176487(40)×10−19  C[7] −4.803×10−10  esu [8]
Magnetic moment:	−1.00115965218111 μB[7]
Spin:	1⁄2

The electron is a subatomic particle carrying a negative electric charge. It has no known components or substructure. Therefore, the electron is generally believed to be an elementary particle.^[2] An electron has a mass that is approximately 1/1836 that of the proton^[9] The intrinsic angular momentum (spin) of the electron is a half-integer value in units of ħ, which means that it is a fermion. The antiparticle of the electron is called the positron. The positron is identical to the electron except that it carries electrical and other charges of the opposite sign. When an electron collides with a positron, both particles may either scatter off each other or be totally annihilated, producing a pair (or more) of gamma ray photons. Electrons, which belong to the first generation of the lepton particle family,^[10] participate in gravitational, electromagnetic and weak interactions.^[11] Electrons, like all matter, have quantum mechanical properties of both particles and waves, so they can collide with other particles and be diffracted like light. However, this duality is best demonstrated in experiments with electrons, due to their tiny mass. Since an electron is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle.^[10]

The concept of an indivisible amount of electric charge was theorized to explain the chemical properties of atoms, beginning in 1838 by British natural philosopher Richard Laming;^[4] the name electron was introduced for this charge in 1894 by Irish physicist George Johnstone Stoney. The electron was identified as a particle in 1897 by J. J. Thomson and his team of British physicists.^[6][12][13]

In many physical phenomena, such as electricity, magnetism, and thermal conductivity, electrons play an essential role. An electron in motion relative to an observer generates a magnetic field, and will be deflected by external magnetic fields. When an electron is accelerated, it can absorb or radiate energy in the form of photons. Electrons, together with atomic nuclei made of protons and neutrons, make up atoms. However, electrons contribute less than 0.06% to an atom's total mass. The attractive Coulomb force between an electron and a proton causes electrons to be bound into atoms. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.^[14]

According to theory, most electrons in the universe were created in the big bang, but they may also be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere. Electrons may be destroyed through annihilation with positrons, and may be absorbed during nucleosynthesis in stars. Laboratory instruments are capable of containing and observing individual electrons as well as electron plasma, whereas dedicated telescopes can detect electron plasma in outer space. Electrons have many applications, including welding, cathode ray tubes, electron microscopes, radiation therapy, lasers and particle accelerators.

• 1 History
  • 1.1 Discovery
  • 1.2 Atomic theory
  • 1.3 Quantum mechanics
  • 1.4 Particle accelerators
• 2 Characteristics
  • 2.1 Classification
  • 2.2 Fundamental properties
  • 2.3 Quantum properties
  • 2.4 Virtual particles
  • 2.5 Interaction
  • 2.6 Atoms and molecules
  • 2.7 Conductivity
  • 2.8 Motion and energy
• 3 Formation
• 4 Observation
• 5 Plasma applications
  • 5.1 Particle beams
  • 5.2 Imaging
  • 5.3 Other
• 6 See also
• 7 Notes
• 8 References
• 9 External links

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations, and a graph of the system is drawn with the oscillating variable as the vertical axis and time as the horizontal axis, the amplitude is visually represented by the vertical distance between the extrema of the curve.

In older texts the phase is sometimes very confusingly called the amplitude.^[1]

• 1 Concepts
  • 1.1 Peak-to-peak amplitude
  • 1.2 Peak amplitude
  • 1.3 Semi-amplitude
  • 1.4 Root mean square amplitude
  • 1.5 Ambiguity
  • 1.6 Pulse amplitude
• 2 Formal representation
• 3 Waveform and envelope
• 4 See also
• 5 Notes

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