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Colour Code of Carbon Resistors


The carbon resistor is the most colorful component in electronic circuits. It has two terminals made of conducting material like copper wire. The terminals don't have polarity. Inside, the terminals are connected to two ends of a carbon rod. The length and diameter of the carbon rod decides resistance of this resistor. This is why these resistors are called carbon resistor.


The value of its resistance is written by a colour code. There are four colour bands, three are close to each other and the fourth one is far away near the end. The colour of three bands represent three digits. Let us say, the first colour represent digit $x$, the second band represent digit $y$ and the third bad represent digit $z$. The value of its resistance is \begin{align} R=xy\times10^{z}. \end{align} The third digit $z$ is called multiplier. Considor a resistor with band colours Brown, Black and Orange, in this sequence. The brown indicates the digit 1, thus $x=1$. The black indicates the digit 0, thus $y=0$. The orange colour indicates the digit 3, thus $z=3$. The resistance of resistor with colour code Brown, Black, Orange is \begin{align} R=xy\times10^{z}=10\times10^3=10,000\;\Omega. \end{align}

The actual resistance will not be 10000 ohm. It will have some error. The maximum possible error is indicated by the fourth band. If it is Golden color then error in resistance is less than 5%, if it is Silver colour then error is less than 10% and if fourth band is absent then error is less than 20%.

The nine digits are represented by 9 colours. Zero by black and 9 by white. There is a funny telegram message to remember the colour code "B B ROY Great Britain Very Good Wife".

Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Grean 5
Blue 6
Violet 7
Grey 8
White 9
Gold 5%
Silver 10%

Problems from IIT JEE

Problem (JEE Mains 2019): A carbon resistance has a following colour code. What is the value of the resistance?

  1. 530 $k\Omega \pm 5\%$
  2. 5.3 $M\Omega \pm 5\%$
  3. 6.4 $M\Omega \pm 5\%$
  4. 64 $k\Omega \pm 10\%$


  1. Ohm's Law
  2. Electrical Resistance
  3. Series and Parallel Arrangements of Resistances
  4. Wheatstone bridge
  5. Symmetry in electrical circuits
  6. Resistance of an Electric Bulb
  7. Specific resistance of the material of a wire using meter bridge and post office box
JEE Physics Solved Problems in Mechanics