IGCSE Physics - 4.3.2 Series and Parallel Circuits

Objective: Explain the advantages of connecting lamps in parallel in a lighting circuit

Introduction

In electrical circuits, components can be connected in series or parallel. This section focuses on the advantages of connecting lamps in parallel, which is a common practice in household wiring.

Series Circuits vs. Parallel Circuits

It's helpful to briefly recall the differences between series and parallel circuits before discussing the advantages of parallel connections.

• Series Circuit: Components are connected end-to-end, so the current flowing through each component is the same. The total resistance is the sum of the individual resistances.
• Parallel Circuit: Components are connected side-by-side, so the voltage across each component is the same. The total current is the sum of the currents through each branch. The reciprocal of the total resistance is the sum of the reciprocals of the individual resistances.

Advantages of Connecting Lamps in Parallel

Connecting lamps in parallel offers several key advantages in a lighting circuit:

1. Independent Operation: Each lamp operates independently. If one lamp burns out, the other lamps will continue to function normally. This is a significant safety and convenience feature.
2. Constant Brightness: The voltage across each lamp in a parallel circuit is the same as the supply voltage. Therefore, each lamp receives the full voltage and will operate at its designed brightness.
3. Adding More Lamps: It's easy to add more lamps to a parallel circuit without affecting the brightness of the existing lamps. Simply connect additional branches of lamps in parallel.

Illustrative Table

The following table summarizes the key differences in how lamps behave when connected in series and parallel.

Feature	Series Connection	Parallel Connection
Current through lamps	Same for all lamps	Divides between branches
Voltage across lamps	Divides between lamps	Same for all lamps (equal to supply voltage)
Brightness of lamps	Dimmer with more lamps	Maintains constant brightness
Failure of one lamp	Entire circuit breaks (all lamps go out)	Other lamps continue to work

Conclusion

Connecting lamps in parallel provides a practical and safe solution for lighting circuits. The independence of each lamp, the maintenance of constant brightness, and the ease of adding more lamps make it the preferred method for domestic lighting.