Resistors are electrical components that we will use quite often. Quite simply they resist the flow of electricity. We will spend more time talking about why we might want to do this in a future lesson. For now we need to focus on how we identify them. It would be convenient if the numerical value was printed on the side of resistors. Unfortunately that’s not what they do. Instead, the value of a resistor must be determined using the colored bands that wrap around them.
We will focus on four banded resistors, but it should be noted that there are resistors with more than four bands as well. If you find resistors in older electronic devices they may only have three bands, but this is very uncommon today.
The fourth band on almost all resistors made today is gold. If your resistor has gold for the first band simply turn the resistor around so it’s the fourth. The fourth band indicates the tolerance. Gold means ±5%. So if the other colors tell us the resistor has a value of 100 ohms, then the true value will lie between 95 and 105 ohms. If the fourth band is silver then it is ±10%.
The first band is the first digit in the resistors value. The second band is the second digit. The third band is the multiplier, but I choose to think of this as the number of zeros to tack on. So, using the conventional way of thinking about it, if you have a resistor with Brown, Black, Red, Gold bands then the first digit of the number would be one, the second number would be zero, the multiplier would be 100, with a tolerance of ±5%. So, 10 x 100 = 1,000 ohms ±5%.
Conventional Color Code
|Color||1st Digit||2nd Digit||Multiplier|
Alternative way of thinking
I instead prefer to think about the third band not as a multiplier, but instead as the number of zeros to tack on. Using only the table below. If you have a resistor with Brown, Black, Red, Gold bands then the first digit 1, second digit 0, then tack on 2 zeros for a value of 1,000 ohms ±5%.
There a couple ways to remember the order the colors go in. First off you might notice that the color portion closely matches the order of colors in the rainbow, “Roy G. Biv”. It simply lacks the indigo. There are also a number of different mnemonics for remembering the order . One is, “Better be right or your great big venture goes wrong.”
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