L> Resistance and ResistivityResistance
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The electric resistance that a circuit ingredient or an equipment is characterized as the ratio of the voltage used to the electric current which flows v it:

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If the resistance is constant over a considerable selection of voltage, climate Ohm"s law, i = V/R, can be offered to guess the behavior of the material. Although the an interpretation above requires DC current and voltage, the same definition holds for the AC applications of resistors.

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Whether or no a material obeys Ohm"s law, the resistance have the right to be defined in terms of its bulk resistivity. The resistivity, and thus the resistance, is temperature dependent. Over sizable ranges of temperature, this temperature dependence have the right to be predicted from a temperature coefficient of resistance.

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The electric resistance that a wire would certainly be meant to be higher for a much longer wire, less for a wire of bigger cross sectional area, and would be expected to depend upon the product out of i beg your pardon the wire is made. Experimentally, the dependency upon these properties is a straightforward one for a wide selection of conditions, and the resistance that a wire can be expressed together

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The aspect in the resistance i beg your pardon takes right into account the nature of the material is the resistivity . Although that is temperature dependent, it can be provided at a given temperature to calculate the resistance of a wire of provided geometry.

It should be listed that the is being presumed that the current is uniform throughout the cross-section the the wire, which is true just for straight Current. For alternative Current there is the phenomenon that "skin effect" in which the present density is maximum in ~ the maximum radius of the wire and also drops for smaller sized radii within the wire. In ~ radio frequencies, this becomes a significant factor in style because the outer part of a cable or cable carries most of the current. The station of resistivity is dubbed conductivity. There are contexts whereby the use of conductivity is an ext convenient.

Electrical conductivity = σ = 1/ρ

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Microscopic check out of resistivity
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The combination rules for any number of resistors in series or parallel have the right to be acquired with the use of Ohm"s Law, the voltage law, and also the existing law.

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Comparison example
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The electric resistance that a wire would be supposed to be greater for a longer wire, much less for a cable of larger cross sectional area, and would be expected to depend upon the product out of which the cable is make (resistivity). Experimentally, the dependency upon these properties is a simple one because that a wide variety of conditions, and the resistance that a wire have the right to be expressed as

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Resistance = resistivity x length/areafunction rcal()fh=document.forms<0>;def();aa=fh.a.value/10000;rrho=fh.rb.value*Math.pow(10,fh.rp.value);ll=fh.l.value;rr=fh.res.value=rrho*ll/aafunction lcal()fh=document.forms<0>;def();aa=fh.a.value/10000;rrho=fh.rb.value*Math.pow(10,fh.rp.value);rr=fh.res.value;ll=fh.l.value=rr*aa/rrho;fh.lc.value=ll/.3048function acal()fh=document.forms<0>;def();rr=fh.res.value;rrho=fh.rb.value*Math.pow(10,fh.rp.value);ll=fh.l.value;aa=fh.a.value=rrho*ll*10000/rr;rad=fh.r.value=Math.sqrt(aa/Math.PI);fh.rc.value=2*rad/2.54function rhocal()fh=document.forms<0>;def();aa=fh.a.value/10000;ll=fh.l.value;rr=fh.res.value;rrho=rr*aa/ll;fh.rb.value=snb(rrho);fh.rp.value=snp(rrho)function ua()fh=document.forms<0>;aa=fh.a.value/10000;rad=fh.r.value=Math.sqrt(fh.a.value/Math.PI);fh.rc.value=2*rad/2.54function ul()fh=document.forms<0>;ll=fh.l.value;fh.lc.value=ll/.3048function ulc()fh=document.forms<0>;llc=fh.lc.value;fh.l.value=llc*.3048function ur()fh=document.forms<0>;rad=fh.r.value;fh.a.value=Math.PI*rad*rad;fh.rc.value=2*rad/2.54function urc()fh=document.forms<0>;rad=fh.r.value=fh.rc.value*2.54/2;fh.a.value=Math.PI*rad*radfunction sn(b,p)return b*Math.pow(10,p)function snp(x)return Math.round(Math.log(x)/Math.LN10)function snb(x)return x/Math.pow(10,snp(x))function svb(b,p)n=sn(b,p);return snb(n)function svp(b,p)n=sn(b,p);return snp(n)function display(x)xx=x;if(x.99*Math.pow(10,5))xx="...";return xxfunction def()fh=document.forms<0>;if (fh.a.value==0)fh.a.value=.0330;if (fh.rb.value==0)fh.rb.value=1.724;if (fh.rp.value==0)fh.rp.value=-8;if (fh.l.value==0)fh.l.value=10;if (fh.res.value==0)fh.res.value=.0522For a cable of length L
= m = ftand area A = cm2corresponding to radius r = cmand diameter customs for common wire gauge comparisonwith resistivity = ρ = x 10^ ohm meterswill have resistance R = ohms.

Enter data and also then click on the quantity you great to calculate in the active formula above. Unspecified parameters will default to values usual of 10 meter of #12 copper wire. Top top changes, the worths will not be required to be constant until you click on the quantity you wish to calculate.

Commonly provided U.S. Cable gauges because that copper wire.

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AWGDiameter(inches)Typical use
100.1019Electric range
120.0808Household circuit
140.0640Switch leads
Standard wire gauges
Resistivities of some metals in ohm-m(x 10-8) at 20°C.
Aluminum2.65Gold2.24
Copper1.724Silver1.59
Iron9.71Platinum10.6
Nichrome100Tungsten5.65
Table that resistivities

The variable in the resistance which takes right into account the nature the the product is the resistivity. Although that is temperature dependent, it can be supplied at a given temperature to calculation the resistance of a wire of provided geometry.

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