(Carbon Resistor Colour Code)
Resistors used in laboratories and for domestic use are of two major types :-
- Wire bound resistors and
- Carbon resistors.
1. Wire bound resistors :-
The selection of materials of wire bound resistors is done in such a way that their resistivity is relatively insensitive to temperature i.e., there is negligible effect of temperature on resistivity. Wire bound resistors are made by alloys like constantan, manganin, nichrome etc. The resistance range of these resistors is relatively small.
2. Carbon Resistor :-
High value resistors are made by semiconductors like carbon. Carbon resistors are compact, inexpensive and these are extensively used in electronic circuits. These are small in size and their resistance values are given using a colour code.
There are generally four co-axial coloured rings(bands) of different colours on carbon resistors. First two rings indicate the first two significant figures respectively of the value of resistance in ohms. The third ring indicates the multiplier in the form of power of 10 in its value. The fourth coloured band indicates the tolerance(i.e., possible
variation in percentage about the indicated values) of the resistance. Sometimes, this last band is absent and that indicates a tolerance of 20%.
The following table gives definite figure, multiplier and tolerance for each colour :-
Draw a colour code for 42 k Ω ± 10% carbon resistance.
According to colour code, colour for digit 4 is yellow, for digit 2 it is red, for 3 colour is orange and 10% tolerance is represented by silver colour.
So colour code should be yellow, red, orange and silver.
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