ECE 211 Electrical Circuits Lab I
LAB #2
Section
Name
Kirchhoff’s Laws
OBJECTIVE:
1. Verify Kirchhoff’s Laws
COMPONENTS AND EQUIPMENT:
1.
2.
3.
4.
5.
Digital multimeter
Variable DC supply
Leads
Resistors
Variable resistor (potentiometer)
THEORY:
The laws governing circuit behavior are based on the meticulous work of the German scientist Gustav
Kirchhoff (1824-1887). Kirchhoff’s laws are derived from conservation laws as applied to circuits.
They tell us that element voltages and currents are forced to behave in certain ways when the devices
are interconnected to form a circuit. These conditions are called connection constraints because they
are based only on the circuit connections and not on the specific devices in the circuit.
Kirchhoff’s Current Law
Kirchhoff’s first law is based on the principle of conservation of charge. Kirchhoff’s Current Law (KCL)
states that the algebraic sum of the currents entering a node is zero at every instant.
Adopting the convention that every current flowing towards the point is positive and that every current
flowing away is negative (or the other way around), this principle can be stated as:
Kirchhoff’s Voltage Law
The second of Kirchhoff’s law is based on the principle of conservation of energy. Kirchhoff’s
Voltage Law (KVL) states that: The algebraic sum of all the voltages around a closed loop is
zero at every instant.
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ECE 211 Electrical Circuits Lab I
LAB #2
Similarly to KCL, it can be stated as:
Part I
Assemble the following circuit:
a) Choose s resistors arbitrarily. List all s resistor value by reading the color code.
b) Measure Vs, V1, V2, …. V8.
c) Verify KVL about abcd, fade, fghj and eckj. Write down the equation for each loop to
verify the KVL. Are there any more loops? Specify if there are any.
d) Is the sum of all the voltages around a loop exactly zero? Why? List at least 3 reasons.
e) Measure the value of the resistors. Then measure the current flowing through each
resistor.
f) Verify KCL by writing equations for the current f l o w i n g i n t o each node.
g) Is the sum of all the currents f l o w i n g into each node exactly zero? Why?
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ECE 211 Electrical Circuits Lab I
LAB #2
Part I I
Assemble the following circuit
R1
Vs
+
5V
-
+
1k
I
R V
-
a) Vary the value of the resistance of the potentiometer and measure and record V and I
for each value. Take enough data points to construct a plot of V vs. I and construct this
plot.
b) If your plot does not intersect the V and/or I axis, “extend” the plot so that it intersects
both. What are the names for the points of intersection?
c) What is the purpose of the resistor labeled R1?
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ECE 211 Electrical Circuits Lab I
LAB #2
Part I I I
-
Given
-
Construct a circuit model like the next one and determine the values of Vs and R
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