9.1 Parallel circuits

• Branches: In the context of electrical circuits, branches refer to individual paths through which electric current flows. Each branch typically contains one or more components (such as resistors, capacitors, or light bulbs) connected in series or parallel.
• Connected in parallel: When components or branches in an electrical circuit are connected in parallel, it means that each component or branch has its terminals connected to the same pair of nodes or junctions. In a parallel connection, the voltage across each component or branch is the same, while the current through each component or branch may vary.
• Connected in series: When components or branches in an electrical circuit are connected in series, it means that the components or branches are connected end-to-end, forming a single path for the current to flow. In a series connection, the same current flows through each component or branch, while the voltage across each component may vary.
• Parallel circuit: A parallel circuit is an electrical circuit configuration where components or branches are connected such that each component or branch has its terminals connected to the same pair of nodes or junctions. In a parallel circuit, the voltage across each component is the same, while the total current entering the circuit is divided among the branches according to their respective resistances or impedances.
• Series circuit: A series circuit is an electrical circuit configuration where components or branches are connected end-to-end, forming a single path for the current to flow. In a series circuit, the same current flows through each component, while the voltage across each component may vary depending on its resistance or impedance.
• IGCSE Circuit Symbols:

  
• IGCSE symbols

  
• Series Circuits:

  • What: In a series circuit, components are connected end-to-end, forming a single path for current flow.
• Series Circuits:

  • When: Series circuits are commonly used in applications where components need to share the same current and where the failure of one component should interrupt the entire circuit.
• Series Circuits:

  • Why: They are used when components need to be operated sequentially or when all components need to have the same current flowing through them.
• Series Circuits:

  • How: Components in a series circuit have the same current flowing through them, and the total resistance is the sum of individual resistances. If one component fails or is removed, the entire circuit is interrupted, and all components cease to function. Series circuits are commonly used in holiday lights, flashlights, and decorative lighting.
• Parallel Circuits:

  • What: In a parallel circuit, components are connected in multiple paths, allowing for independent current flow through each branch.
• Parallel Circuits:

  • When: Parallel circuits are employed when components need to operate independently, share the voltage, and when failure of one component should not affect others.
• Parallel Circuits:

  • Why: They are used to power multiple components simultaneously while allowing each component to have its own current path.
• Parallel Circuits:

  • How: Each branch in a parallel circuit has its own current flow, and the total current is the sum of currents in all branches. If one component fails, it does not affect the operation of others. Parallel circuits are commonly used in homes for electrical outlets, lighting circuits, and appliances.
• Series vs. Parallel:

  • Configuration: Series circuits have components arranged in a single path, while parallel circuits have components arranged in multiple paths or branches.
  • Current: In series circuits, the current is the same through all components, whereas in parallel circuits, the current divides among the branches.
• Series vs. Parallel:

  • Voltage: In series circuits, the voltage divides among the components, while in parallel circuits, all components have the same voltage.
  • Effect of Component Failure: In series circuits, the failure of one component interrupts the entire circuit, whereas in parallel circuits, the failure of one component does not affect others.
• In parallel circuits, the rule states that the current through the cell is equal to the total of the current in all the branches. This means that the current flowing from the cell is divided among the branches.

  A circuit diagram can be used to illustrate this rule. In such a diagram, the readings on ammeters connected to branches in parallel will indicate equal currents, while the sum of the readings on ammeters in different branches will match the reading on the ammeter connected directly to the cell.
• Even if the currents in the branches are different, the total current flowing from the cell will be the sum of the currents in all the branches
• For example, in a circuit with three parallel branches with currents of 1.0 A, 2.0 A, and 0.5 A respectively, the total current flowing from the cell will be 3.5 A (1.0 A + 2.0 A + 0.5 A)
• If the current through the cell is known but the current through one of the branches is missing, it can be calculated using the total current and the currents in the other branches
• This calculation method allows for the determination of the current in any part of the circuit
• Advantages of parallel circuits include the ability for each branch to maintain current flow independently, even if other branches are not functioning. This allows components in the same circuit to be switched on and off independently, enhancing flexibility in operation. Additionally, if a component in one branch fails, it does not affect the operation of components in other branches.
• In a parallel circuit with multiple branches, such as the one depicted in the diagram, each branch can have its own lamp and switch. When a switch in one branch is closed, the corresponding lamp lights up without affecting the operation of lamps in other branches. Similarly, if one lamp stops working, the other lamps remain unaffected.
• Parallel circuits offer versatility in control, as components can be individually switched on and off using switches in each branch. Alternatively, a master switch placed between the cell and the branches allows all components to be switched on or off together. For instance, in the provided circuit diagram, closing switch S4 is necessary for any lamp to light up, while switches S1, S2, and S3 control each lamp independently. Closing S4 with all lamps off turns them all on, and opening S4 with all lamps on turns them all off simultaneously.