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ECE 3710 E: Circuits and
Electronics
Jeff Dugger
Lecture 2: 08/24/00
Review
Q: What is a fundamental property of matter?
A: Charge
Q: How many types of charge? What are they called?
A: Two types of charge , positive and negative
Q: What is the flow of charges called?
A: Current
Q: What provides the motive for charges to move?
A: Electric Potential which is called voltage
+
Current: The flow of charge
Coulombs:
amount of charge
-
+
Current: The flow of charge
Coulombs:
amount of charge
Current:
amount of charge
flowing vs. time
-
I (C/s)
+
Current: The flow of charge
Coulombs:
amount of charge
Current:
amount of charge
flowing vs. time
-
I (A)
Coulombs
Amperes =
Second
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
Mystery
+
Current runs
in a circuit
Circuit
Kirchkoff’s Current Law
12 A
8A
Mystery
+
4A
6A
12 A
8A
Circuit
2A
Kirchkoff’s Current Law
I1 -I2 + I3 -I4 =0
I1
Sum of
=
Currents Entering
I4
I2
I3
Zero
-I1 +I2 - I3 +I4 =0
Sum of
=
Currents Leaving
Zero
I1 + I3 = I2 + I4
Sum of
Sum of
=
Currents Entering
Currents Leaving
Kirchkoff’s Voltage Law
+
+
+
+
0V
V
_4
V
_3
V
_2
V
_1
Kirchkoff’s Voltage Law
+
+
+
+
0V
+V
_ 4
V
_3
V
_2
V
_1
Kirchkoff’s Voltage Law
+
+
+
0V
+
V3+ V4
V
_4
_
V
_2
V
_1
Kirchkoff’s Voltage Law
+
+
+
+
0V
V
_4
V
_3
V2+ V3 + V4
_
V
_1
Kirchkoff’s Voltage Law
+
+
+
+
0V
V
_4
V
_2
V1+ V2 + V3+V4
V
_3
_
Kirchkoff’s Voltage Law
+
V
_
Kirchkoff’s Voltage Law
+
+
V1
_
_ V _
V
+ 2
+ 1
+
V2
_
+
V=V1+V2+V3+V4
+
V3
_
_
+
V4
_
_
+
V3
_
+
V4
_
Sum of voltages around a loop are zero
V1+V2+V3+V4 -V = 0
Summary
• Current is the flow of charge.
• Charge is conserved.
• Kirchkoff’s Current Law (KCL)
is based on charge conservation.
• The tendency of a charge to flow
depends on its potential energy.
• Voltage measures the potential energy of each charge.
• Energy is conserved.
• Kirchkoff’s Voltage Law (KVL)
is based on energy conservation.