A typical reaction path requires the initial reactants to cross an energy barrier, enter an intermediate state and finally emerge in a lower energy configuration. If charge separation is involved, this energy difference can result in an emf. See Bergmann et al. and Transition state.
Faraday's experiment showing induction between coils of wire: The liquid battery (right) provides a current which flows through the small coil (A), creating a magnetic field. When the coils are stationary, no current is induced. But when the small coil is moved in or out of the large coil (B), the magnetic flux through the large coil changes, inducing a current which is detected by the galvanometer (G).
Galvanic cell using a salt bridge
A diagram of Faraday's iron ring apparatus. The changing magnetic flux of the left coil induces a current in the right coil.
The equivalent circuit of a solar cell; parasitic resistances are ignored in the discussion of the text.
Faraday's disk, the first electric generator, a type of homopolar generator.
Solar cell voltage as a function of solar cell current delivered to a load for two light-induced currents IL; currents as a ratio with reverse saturation current I0. Compare with Fig. 1.4 in Nelson.
Alternating electric current flows through the solenoid on the left, producing a changing magnetic field. This field causes, by electromagnetic induction, an electric current to flow in the wire loop on the right.
Faraday's homopolar generator. The disc rotates with angular rate {{mvar|ω}}, sweeping the conducting radius circularly in the static magnetic field {{math|B}} (which direction is along the disk surface normal). The magnetic Lorentz force {{math|v × B}} drives a current along the conducting radius to the conducting rim, and from there the circuit completes through the lower brush and the axle supporting the disc. This device generates an emf and a current, although the shape of the "circuit" is constant and thus the flux through the circuit does not change with time.
A wire (solid red lines) connects to two touching metal plates (silver) to form a circuit. The whole system sits in a uniform magnetic field, normal to the page. If the abstract path {{math|∂Σ}} follows the primary path of current flow (marked in red), then the magnetic flux through this path changes dramatically as the plates are rotated, yet the emf is almost zero. After Feynman Lectures on Physics {{Rp|ch17}}

Faraday's law of induction (briefly, Faraday's law) is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (emf)—a phenomenon known as electromagnetic induction.

- Faraday's law of induction

The general principle governing the emf in such electrical machines is Faraday's law of induction.

- Electromotive force
A typical reaction path requires the initial reactants to cross an energy barrier, enter an intermediate state and finally emerge in a lower energy configuration. If charge separation is involved, this energy difference can result in an emf. See Bergmann et al. and Transition state.

3 related topics with Alpha

Overall

Alternating electric current flows through the solenoid on the left, producing a changing magnetic field. This field causes, by electromagnetic induction, an electric current to flow in the wire loop on the right.

Electromagnetic induction

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Alternating electric current flows through the solenoid on the left, producing a changing magnetic field. This field causes, by electromagnetic induction, an electric current to flow in the wire loop on the right.
Faraday's experiment showing induction between coils of wire: The liquid battery (right) provides a current that flows through the small coil (A), creating a magnetic field. When the coils are stationary, no current is induced. But when the small coil is moved in or out of the large coil (B), the magnetic flux through the large coil changes, inducing a current which is detected by the galvanometer (G).
A diagram of Faraday's iron ring apparatus. Change in the magnetic flux of the left coil induces a current in the right coil.
A solenoid
The longitudinal cross section of a solenoid with a constant electrical current running through it. The magnetic field lines are indicated, with their direction shown by arrows. The magnetic flux corresponds to the 'density of field lines'. The magnetic flux is thus densest in the middle of the solenoid, and weakest outside of it.
Rectangular wire loop rotating at angular velocity ω in radially outward pointing magnetic field B of fixed magnitude. The circuit is completed by brushes making sliding contact with top and bottom discs, which have conducting rims. This is a simplified version of the drum generator.
A current clamp

Electromagnetic or magnetic induction is the production of an electromotive force across an electrical conductor in a changing magnetic field.

Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk Maxwell mathematically described it as Faraday's law of induction.

Pole-mounted distribution transformer with center-tapped secondary winding used to provide "split-phase" power for residential and light commercial service, which in North America is typically rated 120/240 V.

Transformer

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Passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits.

Passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits.

Pole-mounted distribution transformer with center-tapped secondary winding used to provide "split-phase" power for residential and light commercial service, which in North America is typically rated 120/240 V.
Ideal transformer connected with source VP on primary and load impedance ZL on secondary, where 0 < ZL < ∞.
Ideal transformer and induction law
Leakage flux of a transformer
Real transformer equivalent circuit
Instrument transformer, with polarity dot and X1 markings on low-voltage ("LV") side terminal
Power transformer overexcitation condition caused by decreased frequency; flux (green), iron core's magnetic characteristics (red) and magnetizing current (blue).
Laminated core transformer showing edge of laminations at top of photo
Interleaved E-I transformer laminations showing air gap and flux paths
Laminating the core greatly reduces eddy-current losses
Small toroidal core transformer
Windings are usually arranged concentrically to minimize flux leakage.
Cut view through transformer windings.
Legend: 
White: Air, liquid or other insulating medium 
Green spiral: Grain oriented silicon steel 
Black: Primary winding 
Red: Secondary winding
Cutaway view of liquid-immersed transformer. The conservator (reservoir) at top provides liquid-to-atmosphere isolation as coolant level and temperature changes. The walls and fins provide required heat dissipation.
Substation transformer undergoing testing.
An electrical substation in Melbourne, Australia
showing three of five 220 kV – 66 kV transformers, each with a capacity of 150 MVA
Camouflaged transformer in Langley City
Transformer at the Limestone Generating Station in Manitoba, Canada
Schematic of a large oil-filled power transformer 1. Tank 2. Lid
3. Conservator tank 4. Oil level indicator 5. Buchholz relay for detecting gas bubbles after an internal fault 6. Piping
7. Tap changer 8. Drive motor for tap changer 9. Drive shaft for tap changer
10. High voltage (HV) bushing
11. High voltage bushing current transformers
12. Low voltage (LV) bushing
13. Low voltage current transformers
14. Bushing voltage-transformer for metering
15. Core 16. Yoke of the core
17. Limbs connect the yokes and hold them up 18. Coils
19. Internal wiring between coils and tapchanger
20. Oil release valve
21. Vacuum valve
Faraday's experiment with induction between coils of wire
Induction coil, 1900, Bremerhaven, Germany
Faraday's ring transformer
Shell form transformer. Sketch used by Uppenborn to describe ZBD engineers' 1885 patents and earliest articles.
Core form, front; shell form, back. Earliest specimens of ZBD-designed high-efficiency constant-potential transformers manufactured at the Ganz factory in 1885.
The ZBD team consisted of Károly Zipernowsky, Ottó Bláthy and Miksa Déri
Stanley's 1886 design for adjustable gap open-core induction coils
"E" shaped plates for transformer cores developed by Westinghouse

A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force across any other coils wound around the same core.

Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil.

U.S. NRC image of a modern steam turbine generator (STG).

Electric generator

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Device that converts motive power into electric power for use in an external circuit.

Device that converts motive power into electric power for use in an external circuit.

U.S. NRC image of a modern steam turbine generator (STG).
Early Ganz Generator in Zwevegem, West Flanders, Belgium
The Faraday disk was the first electric generator. The horseshoe-shaped magnet (A) created a magnetic field through the disk (D). When the disk was turned, this induced an electric current radially outward from the center toward the rim. The current flowed out through the sliding spring contact m, through the external circuit, and back into the center of the disk through the axle.
Hippolyte Pixii's dynamo. The commutator is located on the shaft below the spinning magnet.
This large belt-driven high-current dynamo produced 310 amperes at 7 volts. Dynamos are no longer used due to the size and complexity of the commutator needed for high power applications.
Ferranti alternating current generator, c. 1900.
A small early 1900s 75 kVA direct-driven power station AC alternator, with a separate belt-driven exciter generator.
The Athlone Power Station in Cape Town, South Africa
Hydroelectric power station at Gabčíkovo Dam, Slovakia
Hydroelectric power station at Glen Canyon Dam, Page, Arizona
Mobile electric generator
Protesters at Occupy Wall Street using bicycles connected to a motor and one-way diode to charge batteries for their electronics

The principle, later called Faraday's law, is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux.