Chapter 2
Resistive Circuits

m2.2 Equivalent Resistance

Find the equivalent resistance between the following terminal pairs in the circuit of Fig. m2.2 under the stated conditions:

1. a-b with the other terminals unconnected,
2. a-d with the other terminals unconnected,
3. b-c with a wire connecting terminals a and d, and
4. a-d with a wire connecting terminals b and c.

Use these component values: R₁ = 10 kΩ, R₂ = 33 kΩ, R₃ = 15 kΩ, R₄ = 47 kΩ, and R₅ = 22 kΩ.

NI Multisim Measurements

Enter the circuit of Figure m2.2 into NI Multisim and use the multimeter to measure each of the four resistances under the stated conditions.

• Place components from the “Virtual Components” palette.
• Place a Simulate → Instruments → Multimeter and choose the ohmmeter setting (“Ω” button).
• Place a ground symbol and attach it to one of the multimeter terminals.

NI myDAQ Measurements

Build the circuit of Figure m2.2. Use the myDAQ DMM (digital multimeter) as an ohmmeter to measure each of the four resistances under the stated conditions.

• Measure and record the resistance of each resistor individually; do this before you connect the resistors together.
• Place the resistors to match the resistor orientations shown in Figure m2.2.
• The circuit need not connect to the myDAQ analog ground AGND terminal; only Multisim requires the ground connection.

Further Exploration with NI myDAQ

Ohm’s Law states that a resistor creates a proportional relationship between its voltage and current v = iR where the resistance R is the proportionality factor. Setting the resistor voltage v to a known value and measuring the resulting current with an ammeter provides another way to measure resistance. Apply this method to measure each of the four resistances and compare with your previous results.

1. Apply the NI myDAQ 5-volt source to the terminals A and D. Use the 5V and DGND (digital ground) terminals, with 5V connected to terminal A and DGND to terminal D.
2. Use the DMM voltmeter to measure the voltage v as it appears at the resistor network, and then record this value. Expect the voltage to be slightly less than 5.0 volts, and also expect that it will vary somewhat from one circuit connection to the next.
3. Use the DMM ammeter to measure the current i flowing into terminal A; record this value, too.
4. Calculate the effective resistance R of the resistor network from your two measurements, and then compare this value to your other measurements.
5. Repeat for the remaining three resistance measurements.