All values of resistance are not available and so it is necessary to obtain some of required values by combining readily available resistors . The two possible ways of combining resistors are:
1. Series combination
2.Parallel Combination
1. Series combination
2.Parallel Combination
Series Combination
A number of resistors are said to be connected in series if they are connected one after another , i.e back to back. If V is the effective potential drop and R the effective resistance , then the effective potential difference across the combination is V=IR. Thus the effective resistance of a series combination of a number of resistors is equal to the sum of resistances of individual resistors.
Parallel Combination
A number of resistors are said to be connected in parallel if they are connected across the same terminals.
Total currents through the combination =the sum of current through each sum of current through each resistors.
I=I1+I2+I3
Therefore, I/R=(I/R1)+(I/R2)+(I/R3).
Color Code of Resistor
The resistance value of commercially available resistors are usually indicated by certain standard color coding. The resistors have a set of coaxial colored rings on it with their significance.The first two bands from the end indicated the first two significant digits and the thrid band indicates the decimal multiplier.The last metallic band indicates the tolerance
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