# 4.2.2 Series and parallel circuits

## Content

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 + R2resistance, 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.

WS 1.4 Explain everyday and technological applications of science; evaluate associated personal, social, economic and environmental implications; and make decisions based on the evaluation of evidence and arguments.

MS 1c - Use ratios, fractions and percentages

MS 3b Change the subject of an equation

MS 3c Substitute numerical values into algebraic equations using appropriate units for physical quantities

MS 3d -Substitute numerical values into algebraic equations using appropriate units for physical quantities