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. Rtotal = R1 + R2 (resistance, R, in ohms, Ω) • Students should be able to: explain qualitatively why adding resistors in series increases 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.