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Parallel Circuits
Electronics Workbench Circuit Simulation Using Multisim

In this tutorial, several circuits from Chapter 5 in the textbook are simulated in EWB using Multisim and the use of instruments is illustrated. In the exercises at the end of the tutorial, you will construct other circuits and run the simulations. In this tutorial, you will

  • Construct EWB circuits
  • Use the EWB meters to measure resistance, current, and voltage
  • Verify Kirchhoff’s current law by simulated measurements
  • Make current divider measurements
  • Use simulated switches in a circuit
Example 5-1

This example illustrates the simulation and resistance measurement for the circuit in textbook Figure 5-22.




Figure 5-1

Solution    The total parallel resistance measured by the multimeter is 13.033, which essentially agrees with the calculated value from textbook Example 5-7.

Simulation    Connect the circuit in Figure 5-1 and run the simulation.



Example 5-2

This example illustrates the simulation of the circuit and the current measurements for the circuit in textbook Figure 5-30.




Figure 5-2

Solution    The measured current values agree with those calculated in textbook Example 5-13. The calculated values were rounded to three significant figures.

Simulation    Connect the circuit in Figure 5-2 and run the simulation.



Example 5-3

This example illustrates Kirchhoff’s current law and the fact that the parallel branch with the least resistance has the most current. The circuit is similar to the one in textbook Figure 5-37, with the voltage source adjusted to provide a total current of 100 mA.




Figure 5-3

Solution    The sum of the two branch currents, I1 and I2, equals the total current IT in accordance with Kirchhoff’s current law. Also notice that the 100 branch has the least current.

Simulation    Connect the circuit in Figure 5-3 and run the simulation.



Multisim/EWB Exercises
  1. Connect the circuit in textbook Figure 5-29 and measure the total current. Compare the measured value with the value calculated in textbook Example 5-12. Now measure the branch currents and verify that their sum is equal to the total current.
  2. Connect the circuit in textbook Figure 5-31 and set the source voltage to the value calculated in textbook Example 5-14. When you measure the total current, it should be 10 mA. Verify that the sum of the branch currents is equal to the total current.
  3. Add a fourth parallel resistor with a value of 1.0 k to the circuit in Exercise 2. Observe what happens to the total current. Check the branch currents in R1, R2, and R3. Are they the same as before? Do all four branch currents add up to the total current?
  4. Construct the automobile light system in textbook Figure 5-26. Change the key that operates the switches so the switches can operate independently.



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