MEASUREMENT OF RESISTANCE USING COLOR CODE

Carbon resistor

When we use resistor, it is necessary to measure resistance of that. But it is not always convenient to measure the resistance of a resistor using device. Usually, the wirewound  resistor are physically big and hence there are enough space to print the resistance value and tolerance value. but carbon resistor are small physically. so it is not convenient to print the value on it. Hence, the manufactures generally use a color code to indicate their value and tolerance.

COLOR CODE:

In this coding system colors are coded as 0,1,2,3,.....8,9.

First, we know the color and its code  then we learn how to calculate the resistance seeing the color printed on carbon resistor.

Color	Code
Black	0
Brown	1
Red	2
Orange	3
Yellow	4
Green	5
Blue	6
Violet	7
Gray	8
White	9

            

 

To remember this you can use this mnemonic -
Black Bro Resident Of Your Greenland Become Very Good Wicketkeeper .
the bold capital letters represent the color Black, Brown, Red, Orange, Yellow, Blue, Violet, White respectively.

Now we learn how to calculate the resistance of a resistor using color code:

 Each resistor is provided 3 or 4 color band. The position of color band is shown in the adjacent diagram. The first band is closer to the edge.
                       

schematic diagram of color band on resistor

Resistor having 4 color band:

If the resistor have 4 color band -

1. The first two color band (closer to the edge ) represents the first two digit os resistance.
2. The 3rd color band represents the number of zeros to be pit after the first two digits.
3. The 4th color band represents the tolerance ( in percentage) .
     Actual resistance of the resistor do not exact same as the calculated result. The amount by which the actual resistance can differ from the color code value is called tolerance.

The tolerance (usually given in percentage ) is represented by 4th band.

Gold  in 4th color band indicate a tolerance ± 5%
Silver in 4th color band indicate a tolerance ± 10%

EXAMPLE:

Here, the resistor has 4 color band.
1st is Orange (3)
2nd is Blue(6)
3rd is Brown (1)
4th is Gold
Therefore, the resistance of the resistor is 360 ohm and tolerance is ± 5%.
Tolerance is ± 5% mean that the actual value of  resistance may not be 360 Ω but it is confirm that the actual value is lying between 342 Ω ( -5% of 360 ohm) to 378 Ω( +5% Of 360 ohm).

Resistor having 3 color band:

• If the resistor have 3 color band and the 3rd band is Gold or Silver  the resistance of that resistor is below 10 ohm.
  1. The first two (closer to the edge ) color band represent the first two digit of the resistance.
  2. 3rd color band represents the fractional decimal multipliers.
     
     When the 3rd band is Gold the first two digit is to be multiplied by 0.1
     When the 3rd band is Silver, the first two digit is to be multiplied by 0.001
     
     EXAMPLE:Suppose, the color band are Brown (1), Green (1), Gold .
     The resistance of the resistor = 15* (0.1) Ω = 1.5 ohm
     
     
• If the resistor have 3 color band but the  3rd band is not Gold or Silver  ( i.e 3rd band is the one of the colors of  Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White) , the value of the resistance is to be calculated as 4 band resistor. In this case  the tolerance is ±20% .
  

Available resistance:

A resistance of any arbitrary value is not available in the market. Only certain fixed carbon resistors are manufactured in large quantities. As a result they become cheaper and easily available. 

• Available resistors of 20% Tolerance are -
  10,15,22,33,47,68 ohms and their decimal multiples (i.e 0.1, 10, 100, 1000 etc.) 
• Available resistors of 10% Tolerance are- 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68,82 and their  decimal multiples ( i.e 1.2, 12, 120, 1200 etc.)

Following is the list of commercially available resistors of ±10% tolerance:

Ω			KΩ			MΩ
1.0	10	100	1.0	10	100	1.0	10
1.2	12	120	1.2	12	120	1.2	12
1.5	15	150	1.5	15	150	1.5	15
1.8	18	180	1.8	18	180	1.8	18
2.2	22	220	2.2	22	220	2.2	22
2.7	27	270	2.7	27	270	2.7
3.3	33	330	3.3	33	330	3.3
3.9	39	390	3.9	39	390	3.9
4.7	47	470	4.7	47	470	4.7
5.6	56	560	5.6	56	560	5.6
6.8	68	680	6.8	68	680	6.8
8.2	82	820	8.2	82	820	8.2