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Measuring Voltage in Series-Parallel Circuits

Figure 1. Measuring voltage across series resistor R1

Figure 2. Measuring voltage across parallel resistor R3

Measuring voltage drops across resistances in series-parallel circuits requires an understanding of both series and parallel circuit behavior.

Figure 1 shows a measurement of the voltage drop across R₁. When set to read voltage, the DMM will read the voltage V_R1. Compare that with Figure 2: a measurement of the voltage drop across R₃, that is, V_R3.

Since R₂ and R₃ are connected in parallel, here the measurement across R₃ will be the same as measuring across R₂. Thus, a measurement across all the resistors would yield V_TOT:

V_TOT = V_R1 + V_R3     or     V_TOT = V_R1 + V_R2

Notice that the circuit is active when making voltage measurements. No leads or wires are lifted, else the circuit behavior would most likely be affected, resulting in incorrect measurements.