The resistors can be combined in two ways to get the desired resistance.
(1) Series Circuit (combination of resistors in series)
(2) Parallel Circuit (Combination of resistors in parallel)
When two or more resistances are connected end to end so that same current flows through each resistor they are said to be connected in series. Suppose three resistors R1, R2 and R3 are joined in series as shown in figure and let the current passing through them be I.
Let V1, V2 and V3 be the potential difference across each resistor respectively. According to ohm’s law:
V1 = I R1
V2 = I R2
and V3 = I R3
If V is the total potential difference between the ends A and D, then
V = V1 + V2 + V3
or V = I R1 + I R2 + I R3
If Rs is the resultant resistance of series circuit, then
V = IRs
or IRs = I R1 + I R2 + I R3
or IRs = I(R1 + R2 + R3)
or Rs = R1 + R2 + R3
So, when some resistors are joined in series, the total resistance of given series of resistors is equal to the sum total of individual resistors.
Test Your Understanding and Answer These Questions:
- What is series circuit?
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