Series and parallel circuits

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

For components connected in series:
- there is the same current through each component
- the total potential difference of the power supply is shared between the components
- the total resistance of two components is the sum of the resistance of each component.

\(R_{total} = R_1 + R_2\)

resistance, R, in ohms, Ω

For components connected in parallel:
- the potential difference across each component is the same
- the total current through the whole circuit is the sum of the currents through the separate components
- the total resistance of two resistors is less than the resistance of the smallest individual resistor.

---

Students should be able to:
- use circuit diagrams to construct and check series and parallel circuits that include a variety of common circuit components
- describe the difference between series and parallel circuits
- explain qualitatively why adding resistors in series increases the total resistance whilst adding resistors in parallel decreases the total resistance
- explain the design and use of dc series circuits for measurement and testing purposes
- calculate the currents, potential differences and resistances in dc series circuits
- solve problems for circuits which include resistors in series using the concept of equivalent resistance.

Students are not required to calculate the total resistance of two resistors joined in parallel.