Resistor values are often written on circuit diagrams using a code system which avoids using a decimal point because it is easy to miss the small dot. Tolerance may be ignored for almost all circuits because precise resistor values are rarely required. If no fourth band is shown the tolerance is ☒0%. For example a 390Ω resistor with a tolerance of ☑0% will have a value within 10% of 390Ω, between 390 - 39 = 351Ω and 390 + 39 = 429Ω (39 is 10% of 390).Ī special color code is used for the fourth band tolerance: Tolerance is the precision of the resistor and it is given as a percentage. The tolerance of a resistor is shown by the fourth band of the color code. Green, blue, silver bands represent 56 times 0.01 = 0.56 Ω Tolerance of resistors (fourth band of color code)
Red, violet, gold bands represent 27 x 0.1 = 2.7Ω The first and second bands represent the digits as normal. To show these small values two special colors are used for the third band: gold which means × 0.1 and silver which means × 0.01. The standard color code cannot show values of less than 10Ω. On circuit diagrams the Ω is usually omitted and the value is written 270K. This resistor has red (2), violet (7), yellow (4 zeros) and gold bands. The fourth band is used to shows the tolerance (precision) of the resistor, this may be ignored for almost all circuits but further details are given below.The third band indicates the number of zeros.The second band gives the second digit.Each color represents a number as shown in the table. Resistors values are normally shown using colored bands. Resistance is measured in ohms, the symbol for ohm is an omega Ωġ Ω is quite small so resistors values are often given in kΩ (Kilo Ohm's) and MΩ (Mega Ohm's). Resistor values - the resistor color code They are not damaged by heat when soldering.
Resistors may be connected either way round. Resistors restrict the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED. Opposition to the flow of current is called resistance and the device or component used for this purpose is called resistor.
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