Inductor and Faidherbe Bridge: Difference between pages

From Wikipedia, the free encyclopedia
(Difference between pages)
Content deleted Content added
VisualWikitext
→‎In electric circuits: capacitor comparison removed
 
CmdrObot (talk | contribs)
339,230 edits
m sp (2): succes→success, troups→troops
 
Line 1: Line 1:
{{Infobox Bridge type
{{mergefrom|Electromagnetic coil|Talk:Inductor#Merger proposal|date=September 2008}}
| type_name = Faidherbe Bridge
| image = Saintlouis pont Faidherbe.jpg
| image_title = General view of Faidherbe Bridge
| ancestor_names = Faidherbe Bridge ([[Pontoon]] [[1865]]-[[1897]])
| sibling_names =
| descendant_names =
| carries = Vehicles, Foot traffic
| span_range = 507.35 [[m]]
| material = [[Metal]]
| movable = yes
| design = ''Nouguier, Kessler et Cie''
| falsework = No
}}


'''Faidherbe Bridge'''<ref>{{fr icon}} [http://www.culture.gouv.fr/culture/inventai/extranet/revue/insitu3/d7/text/d7.pdf Saint–Louis du Sénégal, un enjeu pour le patrimoine mondial]</ref> is a road bridge over the [[Sénégal River]] which links the island of the city of [[Saint-Louis, Senegal|Saint-Louis]] in [[Senegal]] to the [[Africa]]n mainland.
An '''inductor''' is a [[Passive component|passive]] [[Electronic component|electrical component]] with significant [[inductance]].


The city of [[Saint-Louis, Senegal|Saint-Louis]],<ref>{{fr icon}} [http://www.elysee.fr/elysee/elysee.fr/francais/actualites/deplacements_a_l_etranger/2005/fevrier/fiches/senegal/l_ile_saint-louis-le_pont_faidherbe.27707.html Le pont Faidherbe (Ile Saint-Louis)]</ref> the first capital of the [[French West Africa]] is situated on an island near the [[estuary]] of the [[Sénégal River]]. It is separated from the [[Atlantic Ocean]] by a thin 40 km<ref>{{fr icon}} Boubou Aldiouma, [http://www.recherches-africaines.net/document.php?id=344 L’ouverture de la brèche de la Langue de Barbarie et ses conséquences - approche géomorphologique] in ''Recherches Africaines'' (secţiunea 1.1)</ref> strip of sand called the [[Langue de Barbarie]], which starts from [[Nouadhibou]] in [[Mauritania]] and extends all the way to [[Saint-Louis, Senegal|Saint-Louis]]. The suburbs of ''Guet Ndar'' and ''Ndar-Tout'' are situated in this area.
An "ideal inductor" has inductance, but no [[Electrical resistance|resistance]] or [[capacitance]], and does not dissipate energy. A real inductor is equivalent to a combination of a significant ideal inductance, some resistance, and capacitance, usually small. The resistance, a necessary property of a wire except at [[superconductivity|superconducting]] temperatures, may contribute significantly to the [[impedance]], and may dissipate significant [[power (physics)|power]]. At some frequency, usually much higher than the working frequency, a real inductor behaves as a [[resonant circuit]] (due to its [[self capacitance]]).


All the way to the 19th century, access to the island was made through boats. The troops, horses and all the equipment of the [[France|French]] colonial army were moved with some very light boats which could break at any moment.
In practice, inductors are usually implemented by some sort of coiled conductive winding which may surround a [[magnetic core]]. Large inductors used at low frequencies may have thousands of turns around a core; however even a straight piece of wire (i.e., with turns and core reduced to zero) has significant inductance.
[[Image:Electronic component inductors.jpg|thumb|right|300px|Some low-value inductors.]]
[[Image:Inductor.svg|thumb|right|150px|Symbol used to denote an inductor]]


In 1858, [[Louis Faidherbe]], the governor of [[Senegal]],<ref>{{en icon}} [http://www.salysenegal.net/activites/excursions/excursionssaintlouisouis.htm www.salysenegal.net]</ref> inaugurated the ''Bouteville'' boat that was capable of transporting 150 passengers, animals and all kinds of goods. The boat made 10 crosses every day and the costs differed: five [[centimes]] for a person, 50 [[centimes]] for a [[horse]], [[cow]] or [[camel]], and two [[franc]]s for a carrage.
== Physics ==
=== Overview ===
[[Inductance]] (''L'') (measured in [[Henry (unit)|henrys]]) is an effect which results from the [[magnetic field]] that forms around a current-carrying [[Electrical conductor|conductor]] that tends to resist changes in the current. [[Electric current]] through the conductor creates a [[magnetic flux]] proportional to the current. A change in this current creates a change in magnetic flux that, in turn, by [[Faraday's law of induction|Faraday's law]] generates an [[electromotive force]] (EMF) that acts to oppose this change in current. Inductance is a measure of the amount of EMF generated for a unit change in current. For example, an inductor with an inductance of 1 henry produces an EMF of 1 volt when the current through the inductor changes at the rate of 1 ampere per second. The number of loops, the size of each loop, and the material it is wrapped around all affect the inductance. For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high [[Permeability (electromagnetism)|permeability]] such as iron. This can increase the inductance by 2000 times, although less so at high frequencies.


In less than a year it was obvious that this system was overrun and a second boat was introduced but with no success.
=== Hydraulic model ===


Seeing this, a [[frigate]] captain ''Robin'', friend of [[Louis Faidherbe]], asked the print [[Jerome Napoléon]], ''Minister of Algeria and the African Colonies'', the approval for the construction of a floating bridge. Opened on [[July 2]] [[1865]], the bridge had a total length of 680 m (the floatring part of the bridge had a length of 350 m) and a width of four metres. The floating part was formed from 40 metal [[Pontoon bridge|pontoons]] which supported a wooden [[deck]]. Three of these pontoons were specially designed so that it could be created a 20m gap so that large vessels could pass. The bridge was named Faidherbe Bridge by a decree of [[Napoleon III of France]].
Electric current can be modeled by the [[hydraulic analogy]]. An inductor can be modeled by the [[flywheel]] effect of a heavy [[turbine]] rotated by the flow. When water first starts to flow (current), the stationary turbine will cause an obstruction in the flow and high pressure (voltage) opposing the flow until it gets turning. Once it is turning, if there is a sudden interruption of water flow the turbine will continue to turn by inertia, generating a high pressure to keep the flow moving. Magnetic interactions such as in [[transformer#An analogy|transformers]] are not modeled hydraulically.


The opening in [[1885]] of the [[Saint-Louis, Senegal|Saint-Louis]] - [[Dakar]] railway increased the traffic over the bridge. The railway reached all the way to ''[[Soc]]'' and all the goods hauled between the coast and the railway station had to cross over the bridge. To prevent the breakdown of the bridge a special decree was given so that the maximum weight for a vehicle that crosses the bridge to be less than one and a half tonnes.
== Applications ==
[[Image:Choke electronic component Epcos 2x47mH 600mA common mode.jpg|thumb|left|A [[Choke (electronics)|choke]] with two 47mH windings, as may be found in a power supply.]]
Inductors are used extensively in [[analog circuit]]s and signal processing. Inductors in conjunction with [[capacitor]]s and other components form tuned circuits which can emphasize or [[electronic filter|filter]] out specific signal frequencies. This can range from the use of large inductors as chokes in power supplies, which in conjunction with filter [[capacitor]]s remove residual [[hum]] or other fluctuations from the direct current output, to such small inductances as generated by a [[Ferrite (magnet)|ferrite]] bead or [[torus]] around a cable to prevent [[radio frequency interference]] from being transmitted down the wire. Smaller inductor/capacitor combinations provide [[tuned circuit]]s used in radio reception and broadcasting, for instance.


With all its difficulties the bridge remained in service 32 years, until [[1897]] when it was dismantled.
Two (or more) inductors which have coupled magnetic flux form a [[transformer]], which is a fundamental component of every electric [[Public utility|utility]] power grid. The efficiency of a transformer may decrease as the frequency increases due to eddy currents in the core material and skin effect on the windings. Size of the core can be decreased at higher frequencies and, for this reason, aircraft use 400 hertz alternating current rather than the usual 50 or 60 hertz, allowing a great saving in weight from the use of smaller transformers.


==Construction of a new bridge==
An inductor is used as the energy storage device in some [[switched-mode power supply|switched-mode power supplies]]. The inductor is energized for a specific fraction of the regulator's switching frequency, and de-energized for the remainder of the cycle. This energy transfer ratio determines the input-voltage to output-voltage ratio. This ''X''<sub>L</sub> is used in complement with an active semiconductor device to maintain very accurate voltage control.
In the opening of his speech in the ''General Council of Senegal'', governor [[Henri de Lamothe]] proposed that the country should take a loan for infrastructure development. The council agreed on a loan worth five million [[francs|gold francs]], much of the money being for the construction of a metallic bridge between Saint-Louis and ''Soc''. The loan was approved on [[November 21]] [[1892]] by the [[France|French]] president [[Marie François Sadi Carnot]]. A [[France|French]] bank [[CDG]], agreed to give the loan with a low [[interest]] of only four percent.


The [[auction]] was organised by the ''Ministry of Colonies'' which sent to [[Senegal]] five offers for evaluation.
Inductors are also employed in electrical transmission systems, where they are used to depress voltages from lightning strikes and to limit switching currents and [[fault current]]. In this field, they are more commonly referred to as reactors.


After examining each one these offers the ''Faidherbe Bridge Committee'' selected two of them:
As inductors tend to be larger and heavier than other components, their use has been reduced in modern equipment; solid state switching power supplies eliminate large transformers, for instance, and circuits are designed to use only small inductors, if any; larger values are simulated by use of [[gyrator]] circuits.
* the '''Nouguier, Kessler et Cie''' offer;
* the '''Société de Construction de Levallois-Perret''' (owned by [[Gustave Eiffel]]).


The ''Faidherbe Bridge Committee'' and the technical committee in [[Paris]] agreed that the ''Société de Construction de Levallois-Perret'' project was the best for the site. On the other hand the president of the public works in [[Senegal]] and [[Councilmember|councilman]] Jean-Jacques Crespin supported the ''Nouguier, Kessler et Cie'' project. In the end the contract was awarded to ''Nouguier, Kessler et Cie'' at a price of 1.88 million [[francs|gold francs]].
== Inductor construction ==


==Links between Faidherbe Bridge and King Carol I Bridge==
[[Image:Coils.jpg|thumb|150px|Inductors. Major scale in centimetres.]]
[[Image:Faidherbestamp.jpg|thumb|left|200px|Postage stamp from [[Senegal]] 1935 with the Faidherbe Bridge.]]
There are many miths regarding the construction of the Faidherbe Bridge which are present even today and are depicted in some tourist guides. The construction of the bridge is attributed to [[Gustave Eiffel]]. In general it says that the metallic parts of the bridge represents a gift from the [[French Government]] and that the parts were originally designed for the [[King Carol I Bridge]] over the [[Danube River]] in [[Romania]]. Other sources say that the metallic parts were intended for a bridge in [[Austria-Hungary]] over the [[Danube River]] in [[Vienna]] or [[Budapest]]. Finally another myth regarding the beams of the bridge says that the parts were intended for an unspecified site but the vessel transporting mysteriously sunk and the authorities in [[Senegal]] took advantage of this situation and built a local bridge.


The information available in [[Romania]] for the [[King Carol I Bridge]] in [[Cernavoda]] as well as the results of scientists in [[France]] say that the myths are pure fiction.
An inductor is usually constructed as a [[coil]] of [[Electrical conductor|conducting]] material, typically copper wire, wrapped around a [[magnetic core|core]] either of air or of [[ferromagnetic]] material. Core materials with a higher [[Permeability (electromagnetism)|permeability]] than air increase the magnetic field and confine it closely to the inductor, thereby increasing the inductance. Low frequency inductors are constructed like transformers, with cores of [[electrical steel]] [[laminate]]d to prevent [[eddy current]]s. 'Soft [[Ferrite (magnet)|ferrite]]s' are widely used for cores above [[audio frequencies]], since they don't cause the large energy losses at high frequencies that ordinary iron alloys do. This is because of their narrow [[hysteresis]] curves, and their high [[resistivity]] prevents [[eddy current]]s. Inductors come in many shapes. Most are constructed as enamel coated wire wrapped around a [[Ferrite (magnet)|ferrite]] [[bobbin]] with wire exposed on the outside, while some enclose the wire completely in ferrite and are called "shielded". Some inductors have an adjustable core, which enables changing of the inductance. Inductors used to block very high frequencies are sometimes made by stringing a ferrite cylinder or bead on a wire.


First of all the [[Romanian Government]] never finalised the construction contract with the company of [[Gustave Eiffel]] of with another foreign company, taking the decision to build the bridge only with local companies. The [[Cernavoda]] bridge was made entirely by [[Romania]]ns, fulfilling the design of [[Anghel Saligny]], which was also the supervisor of the site. In these conditions, not knowing if the contract will be approved, it is unlikely that a foreign company would build the whole superstructure of the bridge. On the other hand, in [[Austria-Hungary]] there was no need to construct a low bridge like the Faidherbe because of the trade routes.
Small inductors can be etched directly onto a [[printed circuit board]] by laying out the trace in a [[spiral]] pattern. Some such planar inductors use a [[magnetic core#Planar core | planar core]].


==Construction of the metallic bridge==
Small value inductors can also be built on [[integrated circuit]]s using the same processes that are used to make [[transistor]]s. In these cases, aluminium [[interconnect]] is typically used as the conducting material. However, practical constraints make it far more common to use a circuit called a "[[gyrator]]" which uses a [[capacitor]] and active components to behave similarly to an inductor.
The new bridge has a metal [[deck]] formed with [[rivet]]ed [[girder]]s. The bridge has in total eight [[span]]s of which one span of 42.95 [[m]], two spans of 36.55 [[m]] and five spans of 78.26 [[m]]. The total length of the bridge is 507.35 [[m]] and the width is 10.5 [[m]]. The total weight of the [[deck]] is 1,500 [[tonnes]]. The second span from the city is mobile being capable of turning 45 degrees to let small ships to cross.
[[Image:PontFaidherbe2.jpg|thumb|right|Faidherbe Bridge from Saint-Louis.]]


==Opening of the bridge==
== In electric circuits ==
A first opening of the bridge took place in the same day with the ceremonies for the national day of [[Senegal]] in [[July 14]] [[1897]] in the presence of governor Chabié. The ribbon for the access zone was cut by the governor's wife, then the officials walked a short distance to the mobile deck, which was opened to allow the passage of the military ship ''L'Ardent''. 21 cannon shots were fired at [[dusk]] and [[dawn]] to commemorate the construction of the bridge and in that day there were organised ceremonies including [[horse race]]s an [[donkey]] [[Racing|race]]s.


The second opening was on [[October 19]] [[1897]] in the presence of [[André Lebon]], the prime minister of the colonies.
An inductor opposes changes in current. An ideal inductor would offer no resistance to a constant [[direct current]]; however, only [[superconductor|superconducting]] inductors have truly zero [[electrical resistance]].


==Modernisation and rehabilitation works==
In general, the relationship between the time-varying voltage ''v''(''t'') across an inductor with inductance ''L'' and the time-varying current ''i''(''t'') passing through it is described by the [[differential equation]]:
<!-- Deleted image removed: [[Image:Faidherbe5.jpg|thumb|right|150px|Corrosion of the trusses at Faidherbe Bridge]] -->
After more than 100 years since it was opened the bridge is starting to suffer from [[corrosion]] and it is in need of urgent repair.


The rehabilitaion works<ref>{{fr icon}} [http://www.afd.fr/jahia/Jahia/home/activite/Transport/op/edit/pid/934 Sénégal : Projet de réhabilitation lourde du pont Faidherbe à Saint-Louis]</ref> are co financed by the [[French Development Agency]] ('''AFD''') and by the [[Government of Senegal]]. The total cost of the works was estimated to be US$ 27 million, of which US$ 17 million is from '''AFD''' and US$ 10 million is from the government
:<math>v(t) = L \frac{di(t)}{dt}</math>


==Reference==
When there is a [[sinusoidal]] [[alternating current]] (AC) through an inductor, a sinusoidal voltage is induced. The amplitude of the voltage is proportional to the product of the amplitude (<math>I_P</math>) of the current and the frequency ('' f '') of the current.
{{reflist|2}}


==External links==
:<math>i(t) = I_P \sin(2 \pi f t)\,</math>
* {{Structurae|id=s0002738|title=Faidherbe Bridge}}
* [http://www.afddakar.sn/jahia/Jahia/lang/en/home/activite/Eau/pid/996 Bridge on AFD Website]
* [http://www.saintlouisdusenegal.com/english/index.php Bridge on saintlouisdusenegal.com]


==Bibliography==
:<math>\frac{di(t)}{dt} = 2 \pi f I_P \cos(2 \pi f t)</math>
*Bernard Toulier (November 2001). ''Le réveil d’une capitale déchue''. Patrimoine mondial, Saint–Louis du Sénégal, pp. 24–35.
* ''Le pont Faidherbe'', Dakar, GIA, 1967, 16 p.
* Abdoul Hadir Aïdara, «Au coeur de la ville. Le pont Faidherbe», dans ''Saint-Louis du Sénégal d'hier à aujourd'hui'', Grandvaux, 2004, pp. 59-65, ISBN 2-909550-43-5
* Guy Thilmans, ''Le pont Faidherbe'', Editions du CRDS, 2006


{{Commons|Category:Pont Faidherbe}}
:<math>v(t) = 2 \pi f L I_P \cos(2 \pi f t)\,</math>


{{coord missing|Senegal}}
In this situation, the [[Phase (waves)|phase]] of the current lags that of the voltage by 90 degrees. #


[[Category:Bridges in Senegal]]
If an inductor is connected to a [[direct current|DC]] current source, with value ''I'' via a resistance, ''R'', and then the current source short circuited, the differential relationship above shows that the current through the inductor will discharge with an [[exponential decay]]:
[[Category:Bridges completed in 1865]]
[[Category:Bridges completed in 1897]]


{{Link FA|ro}}
:<math>\ i(t) = I (e^{\frac{-tR}{L}})</math>
[[fr:Pont Faidherbe]]

[[he:גשר פדרב]]
=== Laplace circuit analysis (s-domain) ===
[[ro:Podul Faidherbe]]

When using the [[Laplace transform]] in circuit analysis, the transfer impedance of an ideal inductor with no initial current is represented in the ''s'' domain by:

:<math>Z(s) = Ls\, </math>
::: where
:::: ''L'' is the inductance, and
:::: ''s'' is the complex frequency

If the inductor does have initial current, it can be represented by:
* adding a voltage source in series with the inductor, having the value:
:<math> L I_0 \,</math>
(''Note that the source should have a polarity that opposes the initial current'')
* or by adding a current source in parallel with the inductor, having the value:
:<math> \frac{I_0}{s} </math>
::: where
:::: ''L'' is the inductance, and
:::: ''<math>I_0</math> is the initial current in the inductor.

=== Inductor networks ===

{{main|Series and parallel circuits}}
Inductors in a [[Series and parallel circuits|parallel]] configuration each have the same potential difference (voltage). To find their total equivalent inductance (''L''<sub>eq</sub>):

: [[Image:inductors in parallel.svg|A diagram of several inductors, side by side, both leads of each connected to the same wires]]

:<math> \frac{1}{L_\mathrm{eq}} = \frac{1}{L_1} + \frac{1}{L_2} + \cdots + \frac{1}{L_n}</math>

The current through inductors in [[Series and parallel circuits|series]] stays the same, but the voltage across each inductor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total inductance:

: [[Image:inductors in series.svg|A diagram of several inductors, connected end to end, with the same amount of current going through each]]

:<math> L_\mathrm{eq} = L_1 + L_2 + \cdots + L_n \,\! </math>

These simple relationships hold true only when there is no mutual coupling of magnetic fields between individual inductors.

=== Stored energy ===

The [[energy]] (measured in [[joule]]s, in [[SI]]) stored by an inductor is equal to the amount of work required to establish the current through the inductor, and therefore the magnetic field. This is given by:

:<math> E_\mathrm{stored} = {1 \over 2} L I^2 </math>

where ''L'' is inductance and ''I'' is the current through the inductor.

== ''Q'' factor ==

An ideal inductor will be lossless irrespective of the amount of current through the winding. However, typically inductors have winding resistance from the metal wire forming the coils. Since the winding resistance appears as a resistance in series with the inductor, it is often called the ''series resistance''. The inductor's series resistance converts electrical current through the coils into heat, thus causing a loss of inductive quality. The [[Q factor|quality factor]] (or ''Q'') of an inductor is the ratio of its inductive reactance to its resistance at a given frequency, and is a measure of its efficiency. The higher the Q factor of the inductor, the closer it approaches the behavior of an ideal, lossless, inductor.

The Q factor of an inductor can be found through the following formula, where ''R'' is its internal electrical resistance and <math>\omega{}L</math> is Capacitive or Inductive reactance at resonance:

:<math>Q = \frac{\omega{}L}{R}</math>

By using a [[ferromagnetic]] core, the inductance is greatly increased for the same amount of copper, multiplying up the Q. Cores however also introduce losses that increase with frequency. A grade of core material is chosen for best results for the frequency band. At [[VHF]] or higher frequencies an air core is likely to be used.

Inductors wound around a ferromagnetic core may [[saturation (magnetic)|saturate]] at high currents, causing a dramatic decrease in inductance (and Q). This phenomenon can be avoided by using a (physically larger) air core inductor. A well designed air core inductor may have a Q of several hundred.

An almost ideal inductor (Q approaching infinity) can be created by immersing a coil made from a [[superconductor|superconducting]] [[alloy]] in [[liquid helium]] or [[liquid nitrogen]]. This supercools the wire, causing its winding resistance to disappear. Because a superconducting inductor is virtually lossless, it can store a large amount of electrical energy within the surrounding magnetic field (see [[superconducting magnetic energy storage]]).

== Formulae ==

The table below lists some common formulae for calculating the theoretical inductance of several inductor constructions.

{| class="wikitable"
! Construction
! Formula
! Dimensions
|-
! Cylindrical coil<ref name=Nagaoka>{{cite journal|last=Nagaoka|first=Hantaro|authorlink=Hantaro Nagaoka|title=The Inductance Coefficients of Solenoids[http://www.g3ynh.info/zdocs/refs/Nagaoka1909/index.html#31]|date:1909-05-06|publisher=Journal of the College of Science, Imperial University, Tokyo, Japan|page=18|volume=27}}</ref>
| <math>L=\frac{\mu_0KN^2A}{l}</math>
|
*''L'' = inductance in [[Henry (unit)|henries]] (H)
*''μ<sub>0</sub>'' = [[permeability of free space]] = 4''<math>\pi</math>'' × 10<sup>-7</sup> H/m
*''K'' = Nagaoka coefficient<ref name=Nagaoka/>
*''N'' = number of turns
*''A'' = area of cross-section of the coil in [[square metre]]s (m<sup>2</sup>)
*''l'' = length of coil in metres (m)
|-
! rowspan="2"|Straight wire conductor
| <math>L = l\left(\ln\frac{4l}{d}-1\right) \cdot 200 \times 10^{-9}</math>
|
*''L'' = inductance (H)
*''l'' = length of conductor (m)
*''d'' = diameter of conductor (m)
|-
| <math>L = 5.08 \cdot l\left(\ln\frac{4l}{d}-1\right)</math>
|
*''L'' = inductance (nH)
*''l'' = length of conductor (in)
*''d'' = diameter of conductor (in)
|-
! Short air-core cylindrical coil
| <math>L=\frac{r^2N^2}{9r+10l}</math>
|
*''L'' = inductance (µH)
*''r'' = outer radius of coil (in)
*''l'' = length of coil (in)
*''N'' = number of turns
|-
! Multilayer air-core coil
| <math>L = \frac{0.8r^2N^2}{6r+9l+10d}</math>
|
*''L'' = inductance (µH)
*''r'' = mean radius of coil (in)
*''l'' = physical length of coil winding (in)
*''N'' = number of turns
*''d'' = depth of coil (outer radius minus inner radius) (in)
|-
! rowspan="2"|Flat spiral air-core coil
| <math>L=\frac{r^2N^2}{(2r+2.8d) \times 10^5}</math>
|
*''L'' = inductance (H)
*''r'' = mean radius of coil (m)
*''N'' = number of turns
*''d'' = depth of coil (outer radius minus inner radius) (m)
|-
| <math>L=\frac{r^2N^2}{8r+11d}</math>
|
*''L'' = inductance (µH)
*''r'' = mean radius of coil (in)
*''N'' = number of turns
*''d'' = depth of coil (outer radius minus inner radius) (in)
|-
! Toroidal core (circular cross-section)
| <math>L=\mu_0\mu_r\frac{N^2r^2}{D}</math>
|
*''L'' = inductance (H)
*''μ<sub>0</sub>'' = [[Permeability (electromagnetism)|permeability]] of [[vacuum|free space]] = 4''<math>\pi</math>'' × 10<sup>-7</sup> H/m
*''μ<sub>r</sub>'' = relative permeability of core material
*''N'' = number of turns
*''r'' = radius of coil winding (m)
*''D'' = overall diameter of toroid (m)
|}

== See also ==
<div style="-moz-column-count:3; column-count:3;">
* [[Electronic component]]
* [[Capacitor]]
* [[Resistor]]
* [[Memristor]]
* [[Electricity]]
* [[Electronics]]
* [[Gyrator]]
* [[Inductance]] (including ''mutual inductance'')
* [[Induction coil]]
* [[induction cooker|Induction cooking]]
* [[Induction loop]]
* [[Magnetic core]]
* [[Saturable reactor]]
* [[Transformer]]
* [[Reactance (electronics)]]
* [[RL circuit]]
* [[RLC circuit]]
</div>

== Synonyms ==

<!-- Are some of these circular Wikilinks? Should they become hard-redirects back to here? -->
* [[coil]]
* [[Choke (electronics)]]
* [[reactor]]

==Notes==
{{reflist}}

== External links ==

; General
* [http://electronics.howstuffworks.com/inductor1.htm How stuff works] The initial concept, made very simple
* [http://www.lightandmatter.com/html_books/4em/ch07/ch07.html Capacitance and Inductance] - A chapter from an online textbook
* [http://www.mpdigest.com/issue/Articles/2005/aug2005/agilent/Default.asp Spiral inductor models]. Good article on inductor characteristics and modeling.
* [http://www.66pacific.com/calculators/coil_calc.aspx Online coil inductance calculator]. Online calculator calculates the inductance of conventional and toroidal coils using formulas 3, 4, 5, and 6, above.
* [http://www.phys.unsw.edu.au/~jw/AC.html AC circuits]
* [http://www.mikroe.com/en/books/keu/03.htm]- Understanding coils and transforms
* [http://library.thinkquest.org/10784/circuit_symbols.html] - Circuit Schematic Symbols

[[Category:Electromagnetic components]]
[[Category:Energy storage]]

[[af:Induktor]]
[[ar:مستحث]]
[[bs:Zavojnica]]
[[ca:Inductor]]
[[cs:Cívka]]
[[da:Elektrisk spole]]
[[de:Spule (Elektrotechnik)]]
[[et:Induktor]]
[[es:Inductor]]
[[eo:Induktilo]]
[[fr:Bobine (électricité)]]
[[ko:코일]]
[[hr:Zavojnica]]
[[id:Induktor]]
[[is:Spanspóla]]
[[it:Induttore]]
[[he:סליל השראה]]
[[lv:Induktivitātes spole]]
[[hu:Tekercs (elektronika)]]
[[ms:Peraruh]]
[[mn:Индукцийн ороомог]]
[[nl:Spoel]]
[[ja:コイル]]
[[no:Spole (induktans)]]
[[nn:Spole]]
[[pl:Cewka]]
[[pt:Indutor]]
[[ro:Bobină]]
[[ru:Катушка индуктивности]]
[[scn:Ruccheddu]]
[[simple:Inductor]]
[[sq:Induktori]]
[[sk:Cievka (elektrická súčiastka)]]
[[sl:Dušilka]]
[[fi:Kela (komponentti)]]
[[sv:Spole]]
[[ta:மின்தூண்டி]]
[[vi:Cuộn cảm]]
[[tr:Bobin]]
[[uk:Котушка індуктивності]]
[[zh:电感元件]]

Revision as of 21:58, 12 October 2008

Faidherbe Bridge
General view of Faidherbe Bridge
General view of Faidherbe Bridge
AncestorFaidherbe Bridge (Pontoon 1865-1897)
CarriesVehicles, Foot traffic
Span range507.35 m
MaterialMetal
Movableyes
Design effortNouguier, Kessler et Cie
Falsework requiredNo

Faidherbe Bridge[1] is a road bridge over the Sénégal River which links the island of the city of Saint-Louis in Senegal to the African mainland.

The city of Saint-Louis,[2] the first capital of the French West Africa is situated on an island near the estuary of the Sénégal River. It is separated from the Atlantic Ocean by a thin 40 km[3] strip of sand called the Langue de Barbarie, which starts from Nouadhibou in Mauritania and extends all the way to Saint-Louis. The suburbs of Guet Ndar and Ndar-Tout are situated in this area.

All the way to the 19th century, access to the island was made through boats. The troops, horses and all the equipment of the French colonial army were moved with some very light boats which could break at any moment.

In 1858, Louis Faidherbe, the governor of Senegal,[4] inaugurated the Bouteville boat that was capable of transporting 150 passengers, animals and all kinds of goods. The boat made 10 crosses every day and the costs differed: five centimes for a person, 50 centimes for a horse, cow or camel, and two francs for a carrage.

In less than a year it was obvious that this system was overrun and a second boat was introduced but with no success.

Seeing this, a frigate captain Robin, friend of Louis Faidherbe, asked the print Jerome Napoléon, Minister of Algeria and the African Colonies, the approval for the construction of a floating bridge. Opened on July 2 1865, the bridge had a total length of 680 m (the floatring part of the bridge had a length of 350 m) and a width of four metres. The floating part was formed from 40 metal pontoons which supported a wooden deck. Three of these pontoons were specially designed so that it could be created a 20m gap so that large vessels could pass. The bridge was named Faidherbe Bridge by a decree of Napoleon III of France.

The opening in 1885 of the Saint-Louis - Dakar railway increased the traffic over the bridge. The railway reached all the way to Soc and all the goods hauled between the coast and the railway station had to cross over the bridge. To prevent the breakdown of the bridge a special decree was given so that the maximum weight for a vehicle that crosses the bridge to be less than one and a half tonnes.

With all its difficulties the bridge remained in service 32 years, until 1897 when it was dismantled.

Construction of a new bridge

In the opening of his speech in the General Council of Senegal, governor Henri de Lamothe proposed that the country should take a loan for infrastructure development. The council agreed on a loan worth five million gold francs, much of the money being for the construction of a metallic bridge between Saint-Louis and Soc. The loan was approved on November 21 1892 by the French president Marie François Sadi Carnot. A French bank CDG, agreed to give the loan with a low interest of only four percent.

The auction was organised by the Ministry of Colonies which sent to Senegal five offers for evaluation.

After examining each one these offers the Faidherbe Bridge Committee selected two of them:

  • the Nouguier, Kessler et Cie offer;
  • the Société de Construction de Levallois-Perret (owned by Gustave Eiffel).

The Faidherbe Bridge Committee and the technical committee in Paris agreed that the Société de Construction de Levallois-Perret project was the best for the site. On the other hand the president of the public works in Senegal and councilman Jean-Jacques Crespin supported the Nouguier, Kessler et Cie project. In the end the contract was awarded to Nouguier, Kessler et Cie at a price of 1.88 million gold francs.

Links between Faidherbe Bridge and King Carol I Bridge

File:Faidherbestamp.jpg
Postage stamp from Senegal 1935 with the Faidherbe Bridge.

There are many miths regarding the construction of the Faidherbe Bridge which are present even today and are depicted in some tourist guides. The construction of the bridge is attributed to Gustave Eiffel. In general it says that the metallic parts of the bridge represents a gift from the French Government and that the parts were originally designed for the King Carol I Bridge over the Danube River in Romania. Other sources say that the metallic parts were intended for a bridge in Austria-Hungary over the Danube River in Vienna or Budapest. Finally another myth regarding the beams of the bridge says that the parts were intended for an unspecified site but the vessel transporting mysteriously sunk and the authorities in Senegal took advantage of this situation and built a local bridge.

The information available in Romania for the King Carol I Bridge in Cernavoda as well as the results of scientists in France say that the myths are pure fiction.

First of all the Romanian Government never finalised the construction contract with the company of Gustave Eiffel of with another foreign company, taking the decision to build the bridge only with local companies. The Cernavoda bridge was made entirely by Romanians, fulfilling the design of Anghel Saligny, which was also the supervisor of the site. In these conditions, not knowing if the contract will be approved, it is unlikely that a foreign company would build the whole superstructure of the bridge. On the other hand, in Austria-Hungary there was no need to construct a low bridge like the Faidherbe because of the trade routes.

Construction of the metallic bridge

The new bridge has a metal deck formed with riveted girders. The bridge has in total eight spans of which one span of 42.95 m, two spans of 36.55 m and five spans of 78.26 m. The total length of the bridge is 507.35 m and the width is 10.5 m. The total weight of the deck is 1,500 tonnes. The second span from the city is mobile being capable of turning 45 degrees to let small ships to cross.

Faidherbe Bridge from Saint-Louis.

Opening of the bridge

A first opening of the bridge took place in the same day with the ceremonies for the national day of Senegal in July 14 1897 in the presence of governor Chabié. The ribbon for the access zone was cut by the governor's wife, then the officials walked a short distance to the mobile deck, which was opened to allow the passage of the military ship L'Ardent. 21 cannon shots were fired at dusk and dawn to commemorate the construction of the bridge and in that day there were organised ceremonies including horse races an donkey races.

The second opening was on October 19 1897 in the presence of André Lebon, the prime minister of the colonies.

Modernisation and rehabilitation works

After more than 100 years since it was opened the bridge is starting to suffer from corrosion and it is in need of urgent repair.

The rehabilitaion works[5] are co financed by the French Development Agency (AFD) and by the Government of Senegal. The total cost of the works was estimated to be US$ 27 million, of which US$ 17 million is from AFD and US$ 10 million is from the government

Reference

  1. ^ Template:Fr icon Saint–Louis du Sénégal, un enjeu pour le patrimoine mondial
  2. ^ Template:Fr icon Le pont Faidherbe (Ile Saint-Louis)
  3. ^ Template:Fr icon Boubou Aldiouma, L’ouverture de la brèche de la Langue de Barbarie et ses conséquences - approche géomorphologique in Recherches Africaines (secţiunea 1.1)
  4. ^ Template:En icon www.salysenegal.net
  5. ^ Template:Fr icon Sénégal : Projet de réhabilitation lourde du pont Faidherbe à Saint-Louis

External links

Bibliography

  • Bernard Toulier (November 2001). Le réveil d’une capitale déchue. Patrimoine mondial, Saint–Louis du Sénégal, pp. 24–35.
  • Le pont Faidherbe, Dakar, GIA, 1967, 16 p.
  • Abdoul Hadir Aïdara, «Au coeur de la ville. Le pont Faidherbe», dans Saint-Louis du Sénégal d'hier à aujourd'hui, Grandvaux, 2004, pp. 59-65, ISBN 2-909550-43-5
  • Guy Thilmans, Le pont Faidherbe, Editions du CRDS, 2006
Wikimedia Commons has media related to Category:Pont Faidherbe.

Template:Link FA

Retrieved from "https://en.wikipedia.org/w/index.php?title=Inductor&oldid=244855771"