Explain colour code for carbon resistors giving examples
Answers
Colour codes are used on carbon resistors to indicate the value of the resistance.
Resistors have a series of coloured bands, that when decoded, gives the resistance.
The following chart will help:
Black: 0
Brown: 1
Red: 2
Orange: 3
Yellow: 4
Green: 5
Blue: 6
Violet: 7
Grey: 8
White: 9
Gold: 5%
Silver: 10%
Generally resistors have 4 bands, of which the first three give the value of the resistance and the last band (gold or silver) gives the tolerance, i.e. the error in the actual resistance (read more to understand).
To calculate the resistance hold the resistor with the gold or silver band to your right. Find the number equivalent to the first (left-most) band (by matching the colour of the band to its number from the chart above) and multiply by 10. To this number, add the number equivalent to the second band. Basically you should get a two digit number whose first digit is the number equivalent to colour of first band and whose second digit is the number equivalent to colour of second band. Now multiply this two digit number with 10 raised to the power of the number equivalent to the third band. This should give the expected value of the resistor. For example in the image, the first band is green so the first digit is 5 and the second band is blue and hence the second digit is 6. So the two digit number is 56. The third band is orange so we multiply 56 by 10^3 giving us the expected value of resistance as 56×10³ Ω or 5.6 kΩ.
The fourth band gives the error in the actual resistance. For example, the fourth band in the image is gold which is equivalent to 5% and 5% of the expected value of 5.6 kΩ is 280 Ω. Hence the actual value of the resistor can be anywhere between 5.6 kΩ - 280 Ω to 5.6 kΩ + 280Ω.
