Question
Explain the colour code system for resistors with an example.

Answer

$i$. In colour code system, resistors has $4$ bands on it.
Image
$ii$. In the four band resistor, the colour code of the first two bands indicate two numbers and third band often called decimal multiplier.
$iii$. The fourth band separated by a space from the three value bands, indicates tolerance of the resistor.
$iv$. Following table represents the colour code of carbon resistor.
Colours $1^{ st }$ digit $(X)$  $2^{ st }$ digit $(Y)$ Multiplier $\left(\times 10^2\right)$ Tolerance $(%)$
Black $0$ $0$ $\times 10^0$  
Brown $1$ $1$ $\times 10^1$ $\pm 1 \%$
Red $2$ $2$ $\times 10^2$ $\pm 2 \%$
Orange $3$ $3$ $\times 10^3$  
Yellow $4$ $4$ $\times 10^4$  
Green $5$ $5$ $\times 10^5$  
Blue $6$ $6$ $\times 10^6$  
Violet $7$ $7$ $\times 10^7$  
Grey $8$ $8$ $\times 10^8$  
White $9$ $9$ $\times 10^9$  
For Gold     $\times 10^-1$ $\pm 5 \%$
For Silver     $\times 10^-2$ $\pm 10 \%$
No colour       $\pm 20 \%$
$v$. Example:
Let the colours of the rings of a resistor starting from one end be brown, red and orange and gold at the other end. To determine resistance of resistor we have, $x=1, y=2, z=3 \ ($From colour code table$)$
$\therefore \text { Resistance }= xy \times 10^{ z } \Omega \pm \text { tolerance }$
$=12 \times 10^3 \Omega \pm 5 \%$
$=12 k \Omega \pm 5 \%$
$[$Note: To remember the colours in order learn the Mnemonics: $\text{B.B. ROY }$ of Great Britain had Very Good Wife$]$

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