OBJECTIVES
1. To study again the relationship of Ohm's Law.
2. To learn and apply Kirchhoff's Current Law (KCL).
3. To learn and apply Kirchhoff's Voltage Law (KVL).
4. To obtain further practice in electrical measurements.
BACKGROUND & THEORY
Kirchhoff's Current Law (KCL) states that the algebraic sum of currents leaving any node or the algebraic sum of currents entering any node is zero, or:
i1 + i2 + i3 ...in = 0
Also KCL can be stated as the sum of the currents entering a node must equal the sum of the currents leaving a node, or:
i1 + i2 = i3 + i4
As you make a summation of currents, it is suggested that you use currents leaving the node as positive and the currents entering node as negative, or:
-i1 - i2 + i3 + i4 = 0
Kirchhoff's Voltage Law (KVL) states that the algebraic sum of voltages around a closed path is zero, or:
v1 + v2 + v3 ... vn = 0
As you make a summation of voltages, it is suggested that you proceed around the closed path in a clockwise direction. If you encounter a positive (+) sign as you first enter the circuit element, then add the value of that. Conversely, if you first encounter a negative sign as you enter the circuit element, then subtract the value of that voltage.
EQUIPMENT AND PARTS LIST
Digital Multimeter (DMM)
Adjustable D.C. power supply
Circuit bread board
Resistors: 8.2 kW, 15 kW, 39
kW (for Circuit 1 under 4.)
820 W, 1.5 kW, 2.2
kW (for Circuit 2 under 6.)
PROCEDURE
1. Reminder the make, model number, and serial number of each piece of measuring equipment is required on every experiment.
2. Note the color code on each resistor and match it up with its nominal value from the color code cards provided.
3. Measure and record the actual value for each resistor. Make a tabulation showing nominal value versus the measured value. Are the measured values within the specified tolerance of the nominal values?
4. Using the adjustable D.C. power supply and circuit bread board, connect the resistors into a two node circuit as shown below. Note that all four circuit elements are connected between those two nodes, and the source voltage Vs is across each of the three resistors. Let R1 = 8.2 kW, R2 = 15 kW, and R3 = 39 kW.
Circuit 1
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5. Measure all four currents, (Is, I1, I2, and I3), in your actual circuit with Vs = 16 V D.C. Record the actual measured value of the voltage difference between the two nodes.
6. Using the adjustable D.C. power supply and the circuit bread board, connect the resistors into a circuit as shown below. Note that the three resistors are in series so that the same current (Is) flows thru each resistor.
Let R1 = 1.5 kW, R2 = 820 W, and R3 = 2.2 kW
Circuit 2
7. Set the power supply to Vs = 20 V D.C. measure the all four voltages in your actual circuit. Also measure Is.
CALCULATIONS AND COMPARISONS
1. In Circuit 1, use your measured current values to determine if KCL is verified to within the limits of the measuring equipment. Also use Ohm's Law and nominal resistance values to calculate I1, I2, and I3 and then use KCL to calculate Is. Repeat the calculations Using the measured resistance values. Make a chart to compare measured current values with the two sets of calculated values. Include the % differences in this chart. Are the differences between the measured values and the values calculated using the measured resistance values within the accuracy limits of the DMM? Are the differences found using the nominal values for calculations within the tolerance limits of the resistors?
2. In Circuit 2, use your measured voltage values to determine if KVL is verified is verified to within the limits of the measuring equipment. Also use measured value of Is, measured values of resistance, and Ohm's Law to calculate V1, V2, and V3. Make a chart to compare these calculated voltage values with the measured voltage values. Are all differences within the expected limits of accuracy?
CONCLUSIONS (Based on the results from this experiment).
Last updated 02/03/2006