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.

Question: Look at Figure 2. Explain how the potential difference across the resistor and the lamp will change when the switch is closed. (4 marks)

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

Question: Compare the currents I1, I2 and I3 in Figure 2

Question: What is the combined resistance of each pair of resistors in Figure 3?

Figure 3