UMKC CIRCUITS LAB 1

Alexander EckhoffLab Section #6

ME 220 Electric Circuits

Lab Report #1- DC Circuits-Resistive Networks

Alexander G. Eckhoff

February 26, 2015

Introduction


This purpose of this lab was to teach us the basic principles of voltage, current and

resistance measurements using a digital multimeter and a breadboard. With some knowledge

prior to experiment my hypothesis were correct. For part one, I knew the resistors were in series

so they add together to give the equivalent resistance of the circuit. For part 2, using node

analysis and the orientation of current I could calculate voltage at each node. For part 3, with

the 470 ohm resistor removed I knew the voltage across the load would be the voltage across

the 620 ohm resistor.

Methods

Part one:

I was given a bag of resistors to sort through. Using the color band scale I could

determine the resistance of each resistor and then selected a 150, 360, 470, 620 and

820 ohm resistor for our experiments.

Using the sorted out resistors and the breadboard provided I created a circuit where all

the resistors were in series, sharing only one node, making sure none of the resistors

touched.

Leaving the voltage source off I used the DMM on the resistance setting and measured

the equivalent resistance by touching one probe to beginning of circuit and the other to

the end and getting a reading of 2.4, which is 2400 ohms. Through hand calculating the

equivalent resistance was given by R1+R2+R3+R4+R5=2420 ohms. The difference in

the hand calculation and the DMM reading was probably due to the precision of the

DMM.

Then I turned on the voltage source and used the DMM on the voltage setting to

measure the voltage across each resistor. Getting 360 ohm= 1.34V,


820 ohm=3.04V, 150 ohm=.56V, 620 ohm=2.32V, and the 470 ohm=1.75V. My hand

calculations through voltage division were almost exactly the same. The 360

ohm=1.34V, 820 ohm=3.05V, 150 ohm=.56V, 620 ohm=2.31V,

470 ohm=1.75V.

Using the DMM I measured source voltage to be 9.01V and through adding up all of the

voltage drops in my hand calculations I got 9.01V.

Part two:

I used the same resistors I sorted out in part one to create the given circuit in part two of

lab on the bread board, connecting the resistors in both series and parallel.

Using the DMM I measured the voltage at each node by putting one probe at the node

and the other to ground. The reading I got for node one was 3.98V and for node two was

2.83V. In my hand calculations I used node analysis where the sum of the currents

entering and leaving must equal zero and using the system of equations and Matlab I

got node one to be 4.098V and node two to be 2.869V (I1-I2-I3=0, I3-I4-I5=0).

Part three:

Using the same circuit in part two I created a Thevenin equivalent circuit by turning off

the voltage source and removing the load resistance, which was the 470 ohm resistor

and short circuiting it by connecting a patch wire from positive terminal to the negative

terminal.

Using the DMM I measured across the 620 ohm resistor to get the voltage across the

load, which was 240 ohms. For my hand calculations I just added equivalent resistors to

get 243.14 ohms.

To measure the Thevenin voltage I removed the short circuit and turned on the power

source. Connecting the DMM to both sides of the 620 ohm resistor we find the Thevenin


voltage to be 3.85V. In my hand calculations I used mesh analysis to solve for the

currents in each mesh and multiplied I2 by the 620 ohm resistor and found my Thevenin

voltage to be 3.782V.

Results

Measured Calculated Error

Req 2400 Ohms 2420 Ohms .8%

R1 1.34V 1.34V 0%

R2 3.04V 3.05V .3%

R3 .56V .56V 0%

R4 2.32V 2.31V .43%

R5 1.74V 1.75V .57%

Voltage Source 9.01V 9.01V 0%

Node 1 3.98V 4.098V 2.88%

Node 2 2.83V 2.869V 1.36%

Rth 240 Ohms 243.14 Ohms 1.29%

Vth 3.85V 3.78V 1.85%

Conclusion

This week’s lab gave us a hands on understanding of resistance, current and voltage in

circuits, as well as, a hands on learning experience. Using measuring equipment like the DMM I

were able to measure voltages and resistances. Comparing my experimental and theoretical

results, the two were very close to each other with very little error. Some of the error could have

been from the rounding of the DMM, or lack thereof. In this lab I gained a more visual


understanding of how a breadboard works and how current, voltage and resistance interact with

each other.

Appendices

Lab Notes

Part one:

1. Separate equipment, sort resistors by band color to find the 5 resistors for the

experiment.

2. Put resistors in series on bread board and complete the circuit.

3. Using the DMM touch the red probe to the positive terminal and measure the resistance

of each resistor by touching the node of the resistor. (R1-360, R2-820, R3-150, R4-620,

R5-470)

4. Using same method touch the negative terminal with the black probe to find the

equivalent resistance for the whole circuit. (Req-2400)

5. Connect circuit to power source.

6. Use DMM to test voltage across each resistor by touching probes to each side of the

resistor. (R1-1.34, R2-3.04, R3-.56, R4-2.32, R5-1.74)

7. Use DMM to test voltage across the whole circuit by touching probes to positive and

negative terminals. (9.01)

Part two:

1. Connect breadboard with same resistors to simulate the circuit in part two

2. Use DMM and connect probe to ground and the other to each node to find node

voltage in the circuit. (v1-3.98, v2-2.82)


Part three:

1. Using the same circuit from part two, you create a Thevenin equivalent circuit by

removing the 470 ohm resistor and short circuiting It by connecting a patch wire

from positive to negative terminals.

2. Use DMM to measure resistance across the 620 ohm resistor to find Thevenin

resistance. (Rth-240)

3. Remove short circuit and turn on voltage source.

4. Measure voltage across the 620 ohm resistor for Thevenin voltage. (Vth-3.85)


Part one


Part two


Part three


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UMKC CIRCUITS LAB 1