Series & Parallel Circuits

There are two ways of joining electrical components, in series and in parallel. Some circuits include both series and parallel parts.

Series Circuits

A series circuit
  1. There is the same current through each component
  2. The total potential difference of the power supply is shared between the components
  3. The total resistance of two components is the sum of the resistance of each component.  Rtotal = R1 + R2

Parallel Circuits

A parallel circuit
  1. The total current through the whole circuit is the sum of the currents through the separate components
  2. The potential difference across each component is the same
  3. The total resistance of two resistors is less than the resistance of the smallest individual resistor.

The more resistors in series you have, the greater the overall resistance.

Adding resistors in parallel decreases the total resistance because there are more paths for the current to flow through.

The resistor

the potential difference across the resistor becomes 0V

because there is a short circuit across the resistor

The lamp

the potential difference across the lamp increases

because the current increases

Solving problems for circuits which include resistors in series using the concept of equivalent resistance:

I1 = I2 + I3

 I2 = I3

 I1 = 2I2

I1 = 2I3

P: 10 + 10 = 20 Ohms

Q: Less than 10 Ohms

R: 5 + 5 = 10 Ohms

S: Less than 5 Ohms

Figure 3