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Colour coding and tolerance resistances - (Concept)

Resistors are usually very tiny and it is difficult to print resistance values on them. So, colour bands are printed on them to represent the electrical resistance. These colour bands are known as resistor colour codes.

The resistor has a set of coloured concentric rings A, B, C and D it with their significance indicated in table.

'A' denotes the first digit (i.e., the first significant figure), 'B' denotes the second digit (i.e., the second significant figure), 'C' denotes the number of zeros (or power of ten) by which the above two significant figures are to be multiplied. 'D' denotes the tolerance limits (i.e., the error in the value of the resistance).

\begin{array}{|l|l|l|l|l|l|} \hline & \text{Colour} & \text{Strip A} & \text{Strip B} & \text{Strip C-Multiplier} & \text{Strip D-Tolerance} \% \\ \hline \mathrm{B} & \text { black } & 0 & 0 & \times 1 & \\ \hline \mathrm{B} & \text { brown } & 1 & 1 & \times 10 & 1 \\ \hline \mathrm{R} & \text { red } & 2 & 2 & \times 10^{2} & 2 \\ \hline \mathrm{O} & \text { orange } & 3 & 3 & \times 10^{3} & \\ \hline \mathrm{Y} & \text { yellow } & 4 & 4 & \times 10^{4} & \\ \hline \mathrm{G} & \text { green } & 5 & 5 & \times 10^{5} & 0.5 \\ \hline \mathrm{B} & \text { blue } & 6 & 6 & \times 10^{6} & 0.25 \\ \hline \mathrm{V} & \text { violet } & 7 & 7 & \times 10^{7} & 0.1 \\ \hline \mathrm{G} & \text { grey } & 8 & 8 & \times 10^{8} & 0.05 \\ \hline \mathrm{W} & \text { white } & 9 & 9 & \times 10^{9} & \\ \hline \mathrm{G} & \text { gold } & & & \times 0.1 & \pm 5 \\ \hline \mathrm{S} & \text { silver } & & & \times 0.01 & \pm 10 \\ \hline & \text { none } & & & & \pm 20 \\ \hline \end{array}

How to Read Resistor Colour Code?

  • To read them, hold the resistor such that the tolerance band is on your right. The tolerance band is usually gold or silver in colour and is placed a little further away from the other bands.
  • Starting from your left, note down all the colours of the bands and write them down in sequence.
  • Next, use the table given below to see which digits they represent.
  • The band just next to the tolerance band is the multiplier band. So if the colour of this band is Red (representing 2), the value given is 102.

Example: If $A$ is green, $B$ is violet, $C$ is orange and $D$ is silver, resistance is $(57000 \pm 10 \%) \Omega$

Exam Chapter
JEE FOUNDATION Electricity
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