Engneering 1

ENGR 2105 Experiment #1 – Resistor Circuits

1. Introduction and Goals: Demonstrate the voltage-current relationships in DC and AC resistor circuits. Provide experience in using Multisim Live to simulate AC and DC resistor circuits.

2. Equipment List: Multisim Live

3. Theory: Ohm’s Law: V=IR • V = voltage in Volts (V) • I= current in Amperes (A) • R = resistance in Ohms (Ω). • Thus Volts = Amperes x Ohms.

3.1. Analogous Example: Current in a resistor is analogous to water flow in a pipe. Voltage is analogous to pressure and opening and closing the valve is analogous to resistance. A valve that is mostly closed restricts water flow, just as higher resistance value of the resistor lowers current flow for a given voltage.

Figure 1: Electrical Symbols used to draw schematics.

Note: The convention is that “current” is the flow of positive charges from the + (positive) DC to – (negative) DC. We now know that electrons flow as

current from negative to positive, but the convention has persisted.

3.2 In electronics, currents are typically in the milli-Amp (mA, or 1𝑥10−3Amps) or micro-Amp (μA, or 1𝑥10−6 Amps) range.

3.3 Kirchoff’s Current Law (KCL): the algebraic sum of currents through a node = zero (NODE = junction of two or more circuit elements). That is, current into a node equals current out. (By convention, node input current is negative, output current is positive.)

In Figure 2, by KCL: 𝐼1 + 𝐼2 − 𝐼3 = 0

Figure 2

3.4 Kirchoff’s Voltage Law (KVL): the sum of voltages in a closed loop (see Figure 3) is zero: −𝑉𝑆 + 𝐼𝑅1 + 𝐼𝑅2 = 0

Figure 3: Series resistor Circuit Illustrating Kirchoff’s Voltage Law (KVL)

3.7 A DC voltage (battery or power supply) is considered a voltage rise. By convention, voltage rises in a circuit are negative, drops are positive.

4. Experimental Procedure:

4.1 Go to https://www.multisim.com/ and login after creating a free user account.

4.2 Measuring Current in a Single Resistor

4.2.1 In Multisim Live, place a 100 Ω resistor (under the “Passive” menu item) on the “workbench”.

4.2.2 Place a DC Voltage source (under the “sources” menu item) on the workbench and set the voltage to 20 Volts DC.

4.2.3 Using the wiring tool, connect one side of the resistor to one side of the DC power supply, and the other side of the resistor to the other side of the DC power supply.

4.2.4 Place a Ground (under the “Schematic Connectors” menu item) between one side of the resistor and the DC Voltage source.

4.2.5 Place a Current probe (Under the “Analysis and Annotation” menu item) between the other side of the resistor and DC Voltage source.

4.2.6 Start the simulation using the “Play” button and observe the current value, observing any Engineering Notation prefix. Record this value in the Data Sheet.

4.2.7 Stop the simulation. 4.2.8 Using the voltage and the measured current value, calculate the

resistor value using and enter the value in the data sheet. Your calculated resistance should be close to 100 Ω. If it is not close to 100 Ω, something went wrong with the measurement.

4.2.9 Repeat this procedure two using a 270 Ω resistorand then a 330 Ω resisistor.

4.3 Voltage and Current for the Three Resistors in Series 4.3.1 Connect a 100 Ω, 270 Ω, and 330 Ω resistor in series to the 20 Volt

Voltage source. The order of the resistors does not matter.

4.3.2 Measure the Current for the Three Resistors in Series (the current in a series circuit is the same at all points in the circuit, so you can place the current probe anywhere in the circuit. You can experiement with placing the probe at different points to see for yourself.)

4.3.3 Start the simulation and record the current.

4.3.4 Take a screen shot of the running circuit and paste it into a blank document. You will turn this document in along with

your data sheet.

4.3.5 Stop the simulation.

4.3.6 Using the voltage and your measured value for the current, calculate the measured resistance using Ohm’s Law. It should be close to the sum of the resistor values.

4.4 Measuring the Voltage and Current for Three Resistors in Parallel:

4.4.1 Leaving the Voltage Source at 20 Volts, connect the three resistors in parallel (Figures 8).

4.4.2 Place the Current probe between the Voltage Source and the left- most resistor.

4.4.3 Start the simulation. 4.4.4 Record the current. 4.4.5 Take a screen shot of the running simulation and paste into your

screen shot document 4.4.6 Stop the simulation 4.4.7 Use V and I to calculate the resistance of the 3 resistors in

parallel. Is the value close to the theoretical value for VP? (See the worksheet for the instructions to calculate VP.)

4.5 AC Voltage/Current Measurements

4.5.1 Ohm’s and Kirchoff’s laws are also true for alternating current (AC). AC voltages include square waves, triangle waves, etc., but we will use only sinusoidal voltages.

4.5.2 Delete the DC Voltage Source and Replace with an AC Voltage source (under the “Sources” menu item).

4.5.3 Set the AC Voltage source to 20 Volts (Vp = 20 Volts) and 100 Hertz.

4.5.4 Connect the 100 Ω resistor to the AC Voltage source. 4.5.5 Add Voltage and Current probes. 4.5.6 In the “Grapher”, measure the peak voltage and current and

enter these values in the data sheet. 4.5.7 Convert the peak Voltage and Current to RMS values and enter

these values in the data sheet. 4.5.8 Repeat these steps for:

• the 270 Ω and 330 Ω single Resistors.

• The 100 Ω, 270 Ω and 330 Ω resistors connected in series. Take a screen shot of this running simulation and include it in your screen shot document.

• The 100 Ω, 270 Ω and 330 Ω resistors connected in parallel Take a screen shot of this running simulation and include it in your screen shot document.

5 Laboratory Area Cleanup: Wash your hands.

6 Writing the Laboratory Report: A formal lab report is not required.

Experiment #2 Data Sheet

DC Circuit Measurements:

1. Nominal value: 100 Ω resistor 270 Ω resistor 330 Ω resistor

2. Measured Voltage (V):

3. Measured Current (I):

4. Calculated Resistance using 2 and 3 above: 𝑅 =

𝑉

𝐼 =

5. Current reading in series resistors (Amperes) (at 10 VDC):

6. Calculated series resistance using values calculated in step 4:

7. Calculated series resistance using 𝑅 = 𝑉 𝐼 from step 5:

8. Calculated resistance of parallel resistors using values calculated in 4, above:

9. Total current through all three parallel resistors (Amps) (5VDC):

10. Calculated resistance of parallel resistors 𝑅 = 𝑉 𝐼 from step 9:

AC Circuit Measurements

Resistors Measured Peak

Voltage (Volts)

Measured RMS

Voltage (Volts)

Measured Peak

Current (Amps)

Measured RMS

Current (Amps)

Calculated Resistance 𝑹 = 𝑽𝑹𝑴𝑺 𝑰𝑹𝑴𝑺⁄

(Ohms)

100Ω

270Ω

330Ω

3 Resistors In Series

3 Resistors In Parallel

11. How does the calculated resistance in the table above compare to your calculation in step 4? (If they are not close, you are not done.)