Chapter 2
Resistive Circuits

m2.1 Kirchhoff’s Laws

Determine currents I₁ to I₃ and the voltage V ₁ in the circuit of Figure m2.1 with component values I_SRC = 1.8 mA, V _SRC = 9.0 V, R₁ = 2.2 kΩ, R₂ = 3.3 kΩ, and R₃ = 1.0 kΩ.

NI Multisim Measurements

Enter the circuit of Figure m2.1 into NI Multisim and measure the currents I₁ to I₃ and the voltage V ₁.

• Place components from the “Virtual Components” palette
• Place a Simulate → Instruments → Measurement Probe for each current
• Place a Simulate → Instruments → Multimeter to measure the voltage V ₁
• Use interactive simulation Simulate → Run 

NI myDAQ Measurements

Build the circuit of Figure m2.1. Use the myDAQ DMM (digital multimeter) to measure the currents I₁ to I₃ and the voltage V ₁.

• Implement the voltage source V _SRC according to the circuit diagram of Figure  B.2 in Appendix B.
• Measure V _SRC with the myDAQ DMM voltmeter and adjust the potentiometer to set the voltage as close to 9.0 volts as possible.
• Implement the current source I_SRC according to the circuit diagram of Figure B.4 in Appendix B. Use a 680 Ω resistor for the adjustment resistor R.
• Measure I_SRC with the myDAQ DMM ammeter and confirm that the current is close to 1.8 mA. If you desire more precision, use a 1.0 kΩ potentiometer for R₃ and adjust it accordingly.

Further Exploration with NI myDAQ

Resistor R₃ shares the same current as the current source. Study the effect of this resistor on the rest of the circuit.

1. Replace R₃ with a 1.0 kΩ potentiometer.
2. Measure current I₁ and record the range of currents you observe as you adjust the potentiometer over its full range.
3. Repeat for currents I₂ and I₃ and voltage V ₁.
4. Which of the four measured values appears to be independent of the value of R₃?
5. Which of the four measured values appears to depend on the value of R₃?
6. Propose an explanation for your observations.