ResistorCrib - BTEC Electronics

IAN LANG ELECTRONICS

Resistor Code Colours

0 (black)

1 (brown)

2 (red)

3 (orange)

4 (yellow)

5 (green)

6 (blue)

7 (violet)

8 (grey)

9 (white)

Multiplier bands other than the above colours:

Gold: divide by ten

Silver: divide by 100

Tolerance Bands:

Brown: 1%

Red: 2%

Gold 5%

Silver 10%

Resistors have either four bands, or if they are higher precision resistors, five bands encircling the body. Hold the lonely one to the right and read left to right. The lonely one is the one spaced furthest from the others.

1 2 3 4

1 0 0 0 1%

1 0 00 2%

1 2 3 4 5

Band 1, 2 and 3 are significant digits. In the above case they are brown, black and black giving a reading of 100. The fourth band is the multiplier and tells you how many zeroes to put behind the significant digits. In this case it is black, and so no zeroes as black, if you refer to the colour chart on the left, is the colour that represents zero. This then would be a 100 ohm resistor. The tolerance band is the fifth one, and it is brown, giving a tolerance of 1% and therefore a range of 99 to 101 ohms.

Band 1 and band 2 are significant digits. In the above case, as you can see, the bands are brown and black. Refering to the colour key on the left, this reads 1 for the first band and 0 for the second. So far the reading is 10. The third band is the multiplier. This tells you how many zeroes to place behind the significant digits. Above it is black, so no zeroes. This would be a 10 ohm resistor. The fourth band gives tolerance; it is brown and so 1%. The tolerance is plus or minus, so the resistor could be between 9 ohms and 11 ohms and still be good.

In exactly the same way the significant digits above are 1 and 0 to give 10. The multiplier is red, and so two zeroes go behind the significant digits to give a reading of 1000.

This resistor is a 1000 ohm resistor, more correctly stated as 1 kilohm or 1k. The tolerance band is red, giving 2% tolerance or a range of plus or minus 20 ohms

In exactly the same way the significant digits above are 1,0 and 0 to give 100. The multiplier is brown, and so one zero goes behind the significant digits to give a reading of 1000.

This resistor is a 1000 ohm resistor, more correctly stated as 1 kilohm or 1k. The tolerance band is brown, giving 1% tolerance or a range of plus or minus 10 ohms.

The resistor above, has a silver band as the multiplier and so the reading is 010 and we must divide by ten. This is a 0.1 ohm resistor, a very low value indeed.

Other examples:

The resistor above, has a gold band as the multiplier and so the reading is 10 and we must divide by ten. This is a 0.1 ohm resistor, a very low value indeed.

Other examples:

2 2 00 1%

2200 ohm or 2.2k

2 2 0 0 1%

2200 ohm or 2.2k

3 3 0 1%

330 ohm or 330R

2 2 0 1%

330 ohm or 330R

4 7 000 1%

47, 000 ohm or 47k

4 7 0 00 1%

47, 000 ohm or 47k

4 7 0000 1%

470, 000 ohm or 470k

4 7 0 000 1%

470, 000 ohm or 470k

4 7 00000 1%

4,700, 000 ohm or 4.7 Megohm or 4.7M

4 7 0 0000 1%

4,700, 000 ohm or 470k

All resistors are able to handle a maximum power and you should not exceed that power, and in fact you should aim not to exceed 75% of that power. Small resistors are commonly 0.25, 0.6 and 2 Watts, wire-wound types 10W or more, and very large industrial resistors are up to thousands of watts.

To know the power dissipated in a resistor, you must know the current.

The current (I) is given by

I =V/R

current is in amperes, V is the electromotive force in Volts and R the resistance in ohms.

If you had a 9V battery then and ran that through a 1k resistor:

I = 9/1000 = 0.009A

Power in Watts is given by:

W = AV = 0.009 X 9 =0.08 W

which is well within the limits of even a small resistor.

If you ran that 9V through just 10 ohms by the same method of calculation you would get 8.1W and the resistor would burn instantly. Through 100 ohms, 0.81 W and small resistors would burn very quickly.

It is not always easy to see which is the lonely stripe and sometimes it is difficult to tell colours apart. I have difficulty with red and brown sometimes, other people blue and green. White and grey can be problematic too. If you are unsure the best answer is to test with a multimeter. If you are going to do anything serious with electronics this is an indespensible tool and you should have one in your toolbox. I have three and that way I can test various parts of the circuit at the same time. All multimeters can test resistance, voltage and current, and here we are using it for resistance. The dial on the front should be set to the resistance range expected, and resistance is marked with an Omega symbol which looks like this:

The first band on this resistor looks red, but that would give us 260, and that is not a standard value. It might be orange, and that would be 360, which is. To make sure it is a 360 and not a 260 made as a non-standard, we turn the dial to the expected range. We think it's either 260 or 360 so we need to select the correct range- there is 200, too small, 2k, 20k, 200k and 2 meg available. We choose the smallest value into which our expected answer fits, and so that is 2k. Then we put the probes of the multimeter on each end of the resistor, and read

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