Overview
This lecture covers how to calculate total resistance for resistors in series and parallel, and how to use this to determine current or potential difference in a circuit.
Calculating Current and Resistance in Circuits
- The formula for resistance is: Resistance (R) = Potential Difference (V) / Current (I).
- To find current: Current (I) = Potential Difference (V) / Resistance (R).
Resistors in Series
- In a series circuit, total resistance equals the sum of all resistors: R_total = R₁ + R₂ + R₃ + ...
- Current is calculated by dividing potential difference by total resistance.
- Example: For 100Ω and 50Ω in series (total 150Ω) with 20V, current = 20 / 150 = 0.13A.
- Another example: For 20Ω, 15Ω, and 10Ω in series (total 45Ω) with 10V, current = 10 / 45 = 0.22A.
Calculating Potential Difference in Series Circuits
- To find potential difference: Potential Difference (V) = Resistance (R) × Current (I).
- Example: 200Ω + 75Ω in series (275Ω) with 0.5A current, V = 275 × 0.5 = 137.5V.
Resistors in Parallel
- The total resistance of resistors in parallel is less than the smallest individual resistor.
- In parallel, current has multiple paths, increasing total current and reducing total resistance.
- You are not required to calculate total resistance for parallel resistors in this course.
Key Terms & Definitions
- Resistance (R) — the opposition to current flow, measured in ohms (Ω).
- Current (I) — the flow of electric charge, measured in amperes (A).
- Potential Difference (V) — the energy per unit charge, measured in volts (V).
- Series Circuit — circuit where components are connected end-to-end, so current flows through each in turn.
- Parallel Circuit — circuit with branches, so current divides and flows through multiple paths.
- Equivalent Resistance — a single resistor that could replace multiple resistors without changing the circuit’s behavior.
Action Items / Next Steps
- Practice more questions on resistors in series and parallel from the vision workbook.
- Review the formulas for current, resistance, and potential difference.
- Ensure you can describe the behavior of resistors in both series and parallel circuits.