# Resistor Combination Circuits

##### 411

Under normal circumstance m V=IR, where a single resistor is used.

But in most electrical circuits, resistors are used in combinations:

• 1.       Series combination

When 2 resistors are connected to each other such that only one endpoint is connected to one another, then the resistors are said to be in     series with each other.

Since same current flows through both resistors.

Thus potential across R1 , V1=I x R1

Potential across R2, V2=I x R2

Net potential V = V1 + V2

Hence V = IR1 + IR2

V=I(R1+R2)

Hence equivalent Resistance = R1 + R2

In general terms, Req= R1 + R2 + R3 +…..Rn

• 2.       Parallel combination

When 2 resistors or more are connected to each other such that both endpoints are connected to one another, then the resistors are said to be     in parallel with each other.

Since same potential is developed across  both resistors.

Thus current across R1 , I1=V /  R1

Potential across R2, I2=V /  R2

Net current  I= I1 + I2

Hence I = V / R1 + V /R2

Thus equivalent R = R1.R2/(R1+R2)

Hence equivalent Resistance = R1 + R2

In general terms Req = 1/R1 + 1/R2 + …..1/Rn