Automotive Electronics Practice Test

Which method is used to find total resistance in a series-parallel circuit?

1. R = V/I

2. P1*P2/P1+P2 to find parallel resistance, then add series resistance

3. R_total = R1 + R2

4. P = IV

The correct answer is: P1*P2/P1+P2 to find parallel resistance, then add series resistance

In a series-parallel circuit, finding the total resistance involves understanding how resistors behave both in series and parallel configurations. The method described here starts by calculating the equivalent resistance of the resistors that are in parallel using the formula for two resistors: P1 * P2 / (P1 + P2). This is crucial because resistors in parallel combine their resistances in a way that reduces the overall resistance of the circuit. After determining the equivalent resistance of the parallel portion, you then add this value to the resistances of any series components. Resistors in series simply add together, which is represented in the formula R_total = R1 + R2. The combination of these two steps allows one to accurately derive the overall resistance in a mixed circuit configuration. Using the formula R = V/I is applicable for finding resistance in an individual circuit segment, while the formula P = IV relates power to current and voltage but doesn't address how to calculate total resistance directly. As such, starting with parallel resistance calculations and then incorporating series resistance provides a comprehensive method for evaluating total resistance in a circuit that has both series and parallel elements.