Fall 2017
ENSC 220-3
ELECTRIC CIRCUITS I

Lab #1: KVL and KCL

OBJECTIVE:
Using the circuit below, you can verify KVL by showing that the sum of voltages around the loop Vin -> R1 -> R2 is zero. You can also verify KCL by showing that the currents entering node "a" sum to zero.

PREPARATION:

  • Read Lab Handbook Sections:
          2.2.2 Lab Power Supplies
          2.2.3 DMM
          2.3.3 Resistors
          2.4.1 Breadboards
  • Derive equations for all circuit voltages and currents in terms of Vin, R1, R2, and R3.

    EQUIPMENT:

  • Basic lab tools (from your supplies)
  • Breadboard (from your supplies)
  • Digital multimeter (DMM), Fluke 45
  • DC power supply
  • Resistors (assorted, from open lab stock).

    NOTES:

  • Before connecting the power supply to your circuit, preset the voltage and then limit the current to be less than 100 mA. (Use the techniques outlined in the Lab Handbook section 2.2.2.)
  • When making circuit changes, turn down the current on the power supply and turn off the power supply. Turn it on again only after checking the circuit carefully.
  • Check the multimeter setup before hooking it into the circuit. Improper setup can give incorrect readings and/or damage the meter.

    IMPORTANT: When building the circuit, select resistor values such that the power generated in each resistor in the circuit will be well below its 1/4 Watt power dissipation rating.

    METHOD:

    1. Choose appropriate R1, R2, and R3, and measure their values using the DMM.

    2. Construct the circuit and adjust Vin=1.0 V (approximately), under load.

    3. KVL: Calculate the expected voltages across R1 and R2, and then measure them.

    4. KCL: Calculate the expected currents through R1, R2, and R3, and then measure them.

    DISCUSSION:

  • Find the DMM accuracy for measuring DC voltage, current, and resistance.
  • Choose one example from your calculations and show how equipment accuracy and measurement errors propagate through equations to affect expected values.
  • Explain how the measurement process itself affects the resistances, voltages and currents that you are measuring.
  • Reconcile each measurement against the expected value. You should be able to explain any differences within a specified range of certainty.
  • Can you think of a more effective method of confirming KCL?
    Last modified: Fri Sep 22 16:37:50 PDT 2017.