# SS: Series And Parallel Circuits

Show/Hide Sub-topics (D.C. Circuits | O Level)

Series Circuits

Series circuits has the same current through each circuit components BUT different potential difference across each circuit components.

Same Current • In a series circuit, the flow of charges has only one path to follow. The flow of charge passes through each component in turn.
• Therefore, in a series circuit, the current at every point is the same.
• Adding a new component to the series circuit reduces the current flow throughout because of the added resistance of the new component.

Different potential difference • Potential difference (p.d.) between two points in a circuit is caused by the energy dissipation in the circuit elements connected between those two points. Energy is a scalar quantity. It can be added to get the total energy dissipation in a circuit.
• In a series circuit, the sum of the potential difference across the sinks (i.e. the bulbs) is equal to the sum of the e.m.f.s across the sources (i.e. the battery).
• In a series circuit, the sum of the potential difference across the bulbs is equal to the potential difference across the battery.
• In a series circuit, the highest potential difference occurs across a component with the largest resistance. (Disregarding the potential difference across the battery)
• The potential difference between the ends of any of the pieces of connecting wire is effectively zero because there is almost no loss of potential energy.

Parallel Circuits

Parallel circuits has the different current through each branch (same current through the circuit components within the branch) BUT same potential difference across each branch. (different potential difference across the circuit components within the branch)

Different currents • Instead of wiring components in series, they can be connected in parallel. Parallel connection offers different paths for the flow of charges, but the total flow of charges from the source remains unchanged.
• Therefore, in a parallel circuit, the current from the source is the sum of the currents in the separate branches.
• In the parallel circuit shown, if one lamp is removed, the others still light up. This is why most household lighting circuits are connected in parallel.
• In a parallel circuit, the largest current will pass through the branch with the smallest effective resistance.
• At a junction in a circuit, the total current entering a junction is equal to the total current leaving the junction. This is the conservation of charge.

Same potential difference • In a parallel circuit, two or more components are connected between two points of the circuit. The potential difference across a component is the potential difference between the two points and is equal to the potential difference of any other component connected in between.
• Therefore, the potential difference across separate branches of a parallel circuit is the same. 