# 3.7.4: Procedure

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1. Consider the circuit of Figure 8.3.1. R5 and R6 form a simple series connection. Together, they are in parallel with R4. Therefore the voltage across R4 must be the same as the sum of the voltages across R5 and R6. Similarly, the current entering node C from R3 must equal the sum of the currents flowing through R4 and R5. This three resistor combination is in series with R3 in much the same manner than R6 is in series with R5. These four resistors are in parallel with R2, and finally, these five resistors are in series with R1. Note that to find the voltage at node B the voltage divider rule may be used, however, it is important to note that VDR cannot be used in terms of R1 versus R2. Instead, R1 reacts against the entire series-parallel combination of R2 through R6. Similarly, R3 reacts against the combination of R4, R5 and R6. That is to say R5 and R6 load R4, and R3 through R6 load R2. Because of this process note that $$V_D$$ must be less than $$V_C$$, which must be less than $$V_B$$, which must be less than $$V_A$$. Thus the circuit may be viewed as a sequence of loaded voltage dividers.

2. Construct the circuit of Figure 8.3.1 using R1 = 1 k, R2 = 2.2 k, R3 = 3.3 k, R4 = 6.8 k, R5 = 10 k, R6 = 22 k and E = 20 volts. Based on the observations of Step 1, determine the theoretical voltages at nodes A, B, C and D, and record them in Table 8.5.1. Measure the potentials with a DMM, compute the deviations and record the results in Table 8.5.1.

3. Based on the theoretical voltages found in Table 8.5.1, determine the currents through R1, R2, R4 and R6. Record these values in Table 8.5.2. Measure the currents with a DMM, compute the deviations and record the results in Table 8.5.2.

4. Consider the circuit of Figure 8.3.2. In this bridge network, the voltage of interest is $$V_{AB}$$. This may be directly computed from $$V_A − V_B$$. Assemble the circuit using R1 = 1 k, R2 = 2.2 k, R3 = 10 k, R4 = 6.8 k and E = 10 volts. Determine the theoretical values for $$V_A$$, $$V_B$$ and $$V_{AB}$$ and record them in Table 8.5.3. Note that the voltage divider rule is very effective here as the R1 R2 branch and the R3 R4 branch are in parallel and therefore both “see” the source voltage.

5. Use the DMM to measure the potentials at A and B with respect to ground, the red lead going to the point of interest and the black lead going to ground. To measure the voltage from A to B, the red lead is connected to point A while the black is connected to point B. Record these potentials in Table 8.5.3. Determine the deviations and record these in Table 8.5.3.

3.7.4: Procedure is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by James M. Fiore.