GCSE Physics Tutorial: Qualitative Explanation of Series and Parallel Resistance
The total resistance in an electrical circuit changes when resistors are added either in series or in parallel. Understanding why adding resistors in series increases the total resistance while adding resistors in parallel decreases the total resistance, is essential in circuit analysis. In this tutorial, we will provide a qualitative explanation for these changes.
1. Resistors in Series: When resistors are connected in series, they are placed one after the other, forming a single path for current to flow through. The current passing through each resistor is the same because there is no branching of the current path. The key points to note are:
Resistance Addition: In a series circuit, the total resistance increases as more resistors are added. This is because the total resistance is the sum of the individual resistances of all the resistors in series.
Limited Current Flow: With resistors in series, each resistor restricts the current flow, making it more difficult for the current to pass through the circuit. As a result, the total resistance is higher compared to a single resistor.
2. Resistors in Parallel: When resistors are connected in parallel, they are placed side by side, each having both its positive and negative terminals connected together. Each resistor has its own path for current to flow through. The key points to note are:
Resistance Division: In a parallel circuit, the total resistance decreases as more resistors are added in parallel. This is because the total resistance is calculated differently for resistors in parallel compared to series.
Increased Current Flow: With resistors in parallel, the current is divided among the branches, which provides additional paths for current to flow. As a result, the overall resistance is reduced compared to a single resistor.
3. Intuitive Understanding: Think of resistors in series as a narrow pathway that restricts the flow of water (current). Each resistor adds more obstacles, making it harder for the water to flow smoothly, increasing the overall resistance.
On the other hand, consider resistors in parallel as multiple streams of water flowing independently side by side. Each stream has less restriction, and the total flow of water (current) increases, resulting in decreased resistance.
4. Formula for Total Resistance:
Resistors in Series: The total resistance (R_total) in a series circuit is the sum of the individual resistances (R₁, R₂, R₃, ...) of each resistor:
R_total = R₁ + R₂ + R₃ + ...Resistors in Parallel: The total resistance (R_total) in a parallel circuit is calculated using the formula:
1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ...
5. Summary: In summary, adding resistors in series increases the total resistance because they restrict the current flow, while adding resistors in parallel decreases the total resistance due to the division of current among the parallel branches. Understanding these qualitative explanations will help you analyse circuits with multiple resistors and design circuits with the desired resistance values for specific applications.
Looking for a more dynamic learning experience?
Explore our engaging video lessons and interactive animations that GoPhysics has to offer – your gateway to an immersive physics education!
