how to tell what resistance a resistor is

If you retrieve those colorful bands on your resistors are at that place just for testify, think again! Those bands tell you the value of the resistor. Before you lot can decode the resistor value, y'all demand to know a little more than nearly resistors.

There are two main types of resistors:

• Standard resistors accept four color bands. Iii of the bands tell you the nominal value, which means the value the resistor was designed to take. The 4th band tells yous the tolerance of the resistor, which indicates how far off the nominal value the actual resistance could exist. (The manufacturing procedure isn't perfect, so most resistors are a little off.)

  For case, yous may purchase what you recall is a 100 Omega resistor, but the bodily resistance almost probable isn't exactly 100 Omega. It may exist 97 or 104 Omega, or another value close to 100 Omega. For most circuits, "close" is expert enough.

• Precision resistors, which have more than precise values than standard resistors, accept 5 color bands. 4 of the bands tell you the nominal value. The fifth band tells yous the tolerance.

  You can count on the bodily resistance of a precision resistor existence actually shut to its nominal value. So, if you purchase a 100 Omega precision resistor, chances are its actual value is within 1 or ii of 100 Omega.

The following effigy shows a diagram of the color code of a standard (four-band) resistor. You utilize this colour code to figure out the nominal value and tolerance of a standard resistor.

Decoding the nominal value of a resistor

Here's how you use the color lawmaking to figure out the nominal value of the resistor (refer to the figure):

1. Decide which band is the first band.

   Compare the ends of the resistor. Normally, the colored band at one end is closer to that end than is the colored band at the other end. If that is the case, the band that is closest to ane end of the resistor is the start band.

   If you tin can't determine which is the outset band, look at the two outer bands. If one of the outer bands is silverish or aureate, that band is probably the last ring, and then the start band is at the other stop.

2. Look upwardly the color of the get-go band in the column labeled "1st digit" and find the number associated with that color.

   This number is the first digit of the resistance. In the resistor shown in the preceding figure, the first band is xanthous, so the first digit is 4.

3. Look upwards the colour of the 2nd band in the column labeled "2d digit" and find the number associated with that color.

   This number is the second digit of the resistance. In the resistor shown in the preceding figure, the 2nd band is violet, so the second digit is 7.

4. Look upward the color of the 3rd band in the column labeled "X" and find the number associated with that color.

   This number is the multiplier. In the resistor shown in the preceding effigy, the 3rd band is dark-brown, so the multiplier is xⁱ (which is 10).

5. Put the first ii digits side-by-side to form a 2-digit number.

   For the resistor shown in the preceding effigy, the kickoff two digits are 4 and 7, and so the 2-digit number is 47.

6. Multiply the two-digit number past the multiplier.

   This gives you the nominal value of the resistor in ohms. In the resistor shown in the preceding figure, the 2-digit number is 47 and the multiplier is ten, so the nominal value is

   

An like shooting fish in a barrel manner to multiply a whole number by a power of x (that is, 10⁰, 10¹, 10², 10³, and and so on) is to but suspend (meaning tack on to the finish) the whole number with zeros, and utilize the exponent (which is the small, raised number adjacent to the 10) to tell you how many zeros to append. Hither are two examples:

• 22 x 10^three. The exponent is iii, so you stick 3 zeros to the right of 22, and you get 22,000. (The multiplier in this case is 10³, which is 1,000.)

• 56 x 10⁰. The exponent is 0, so you stick 0 zeros to the right of 56, and you lot get 37. (The multiplier in this instance is x⁰, which is 1, because whatsoever number raised to the 0th power equals 1.)

If you have a precision (v-ring) resistor (which you're unlikely to use for projects in Electronics For Kids For Dummies), the third band gives you the third digit of the resistance and the fourth band gives y'all the multiplier.

Reading a resistor'south tolerance

To figure out how far off from the nominal value the bodily resistance could be, you look at the fourth band on a standard resistor (or the fifth band on a precision resistor). Refer to the preceding figure for the color code for the tolerance of a resistor.

Say that the fourth band of the 470 Omega resistor yous have called for a detail project is gold. The colour, gold, in the column labeled "tolerance" in the figure represents a tolerance of 5 percent. Because 5 percent of 470 is 23.v, the actual resistance could be as much as 23.5 Omega higher or lower than 470 Omega. So the actual value of the resistance could be whatsoever value from 446.v to 493.5 Ω.

Most standard resistors have tolerances of v%, 10%, or 20%, and most precision resistors take tolerances of 1% or 2%. For the majority of circuits — and in all the projects in Electronics For Kids For Dummies — information technology'southward okay to use a standard resistor. For certain circuits, it's of import to apply a precision resistor with a lower tolerance.

The following effigy shows you two more examples of resistors and their values.

You tin can measure out the actual value of a specific resistor using a device called a multimeter. For case, when you use a multimeter to measure a 470 Omega resistor with a 5 percent tolerance, you might plant that the actual value is 481 Omega.

Almost This Commodity

Near the volume writer:

Cathleen Shamieh is an electric engineer and a loftier-tech writer with extensive engineering and consulting experience in the fields of medical electronics, speech processing, and telecommunications.

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• General (Electronics) ,

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Source: https://www.dummies.com/article/technology/electronics/general-electronics/how-to-read-resistor-values-138047

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