Resistors: Difference between revisions
(added resistor pic and colour codes table - still need resistor types/construction) |
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:"V" is the potential difference between the ends of the resistor in volts, and | :"V" is the potential difference between the ends of the resistor in volts, and | ||
:"R" is the resistance of the resistor, measured in ohms | :"R" is the resistance of the resistor, measured in ohms | ||
== Resistor colour bands == | |||
The resistance of a resistor is coded into a series of coloured bands along its length: | |||
* band '''A''' is first significant figure of component value | |||
* band '''B''' is the second significant figure | |||
* band '''C''' is the decimal multiplier | |||
* band '''D''' if present, indicates tolerance of value in percent (no color means 20%) | |||
[[Image:170px-Resistor_bands.svg.png]] | |||
{| class="wikitable" | |||
!Color!!1<sup>st</sup> band!!2<sup>nd</sup> band!!3<sup>rd</sup> band (multiplier)!!4<sup>th</sup> band (tolerance)!!Temp. Coefficient | |||
|- style="background:black; color:white" | |||
| <font color=white>[[Black]]</font> || 0 || 0 ||×10<sup>0</sup>|| || | |||
|- style="background:#B8860B; color:white" | |||
|<font color=white>[[Brown]]</font> ||1||1||×10<sup>1</sup>||±1% (F) ||100 ppm | |||
|- style="background:#FF0000; color:white" | |||
|<font color=white>[[Red]]</font> ||2||2||×10<sup>2</sup>||±2% (G) ||50 ppm | |||
|- bgcolor = "#FFA500" | |||
|[[Orange (color)|Orange]]||3||3||×10<sup>3</sup>|| ||15 ppm | |||
|- bgcolor = "#FFFF00" | |||
|[[Yellow]]||4||4||×10<sup>4</sup>|| ||25 ppm | |||
|- bgcolor = "#9ACD32" | |||
|[[Green]] ||5||5||×10<sup>5</sup>||±0.5% (D) || | |||
|- bgcolor = "#6495ED" | |||
|[[Blue]] ||6||6||×10<sup>6</sup>||±0.25% (C)|| | |||
|- bgcolor = "#EE82EE" | |||
|[[Violet (color)|Violet]]||7||7||×10<sup>7</sup>||±0.1% (B) || | |||
|- bgcolor = "#A0A0A0" | |||
|[[Grey|Gray]] ||8||8||×10<sup>8</sup>||±0.05% (A)|| | |||
|- bgcolor = "#FFFFFF" | |||
|[[White]] ||9||9||×10<sup>9</sup>|| || | |||
|- bgcolor = "#FFD700" | |||
|[[Gold (color)|Gold]] || || ||×10<sup>-1</sup> ||±5% (J) || | |||
|- bgcolor = "#C0C0C0" | |||
|[[Silver (color)|Silver]]|| || ||×10<sup>-2</sup> ||±10% (K) || | |||
|- | |||
|None || || || ||±20% (M) || | |||
|} |
Revision as of 00:39, 8 March 2008
Resistance and Resistivity
Resistance (R) is the measure of how much an object - a resistor - opposes the flow of electric current. The resistance of an object is measured in Ohms (<math>\Omega</math>)
Resistivity (<math>\Rho</math>) is a measure of how strongly a material opposes the flow of electric current. Resistivity is measured in ohm metres (<math>\Omega</math>m). Related wiki page: table of resistivities
The relationship between resistance and resistivity is:
- <math>R = {l \cdot \rho \over A} \,</math>
where
- "l" is the length of the object
- "A" is the cross sectional area of the object (assuming constant), and
- "ρ" is the resistivity of the material
Resistors
A resistor is a passive electrical device that has been manufactured specifically to add resistance to a circuit, to effect a voltage drop.
The mathematical equation that describes the relationship between resistanece, voltage drop and current through a resistor is known as Ohms Law
- <math>I = \frac{V}{R}</math>
where
- "I" is the current in amperes,
- "V" is the potential difference between the ends of the resistor in volts, and
- "R" is the resistance of the resistor, measured in ohms
Resistor colour bands
The resistance of a resistor is coded into a series of coloured bands along its length:
- band A is first significant figure of component value
- band B is the second significant figure
- band C is the decimal multiplier
- band D if present, indicates tolerance of value in percent (no color means 20%)
Color | 1st band | 2nd band | 3rd band (multiplier) | 4th band (tolerance) | Temp. Coefficient |
---|---|---|---|---|---|
Black | 0 | 0 | ×100 | ||
Brown | 1 | 1 | ×101 | ±1% (F) | 100 ppm |
Red | 2 | 2 | ×102 | ±2% (G) | 50 ppm |
Orange | 3 | 3 | ×103 | 15 ppm | |
Yellow | 4 | 4 | ×104 | 25 ppm | |
Green | 5 | 5 | ×105 | ±0.5% (D) | |
Blue | 6 | 6 | ×106 | ±0.25% (C) | |
Violet | 7 | 7 | ×107 | ±0.1% (B) | |
Gray | 8 | 8 | ×108 | ±0.05% (A) | |
White | 9 | 9 | ×109 | ||
Gold | ×10-1 | ±5% (J) | |||
Silver | ×10-2 | ±10% (K) | |||
None | ±20% (M) |