Overview of ENGR 220
Circuits 1
Fall 2005
Harding University
Jonathan White
Sections
Basic Concepts
 Resistive Circuits
 Capacitors/Inductors
 RC, RL, and RLC circuits
 OP Amps
 Intro. to AC Circuits
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Basic Concepts
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Charge – electrical property of matter that exists
because of an excess or deficiency of electrons
Current – rate of flow of charge (electrons)
Voltage – amount of energy available to move
electrons from one point to another in a circuit
Energy – fundamental capacity to do work
Power – rate of energy usage
Electron shells / Valence electrons /
Conductors/Semiconductors/Insulators / Circuit
symbols
Basic Concept Questions
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How many coulombs of charge do 50 x 1031 electrons
possess?
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500 joules of energy are used to move 100 C of charge
through a resistor. What’s the voltage across the
resistor?
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How much energy does a 12 V battery in your car use to
move 2.5 C through the electrical circuit?
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.6 C passes a point in 3 s. What’s the current in
amperes?
Resistive Circuits – Basic Laws
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Resistor – Device that opposes the flow of
current
Ohm’s Law: v = iR
Kirchoff’s voltage law: Sum of voltages around a
closed loop is zero
Kirchoff’s current law: Sum of currents entering a
node is equal to the currents leaving a node
Parallel resistors: Req = (R1R2) / (R1 + R2)
Series resistors: Req = (R1 + R2)
Power: P = I2R, P = VI, P = V / I
Basic Law Questions
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In the circuit below, what’s V1 and V2 ?
Resistive Circuits - Analysis
Nodal Analysis - Choose a node; setup
current and voltage equations using KCL
and Ohm’s Law; solve for unknown
voltages
 Mesh Analysis – Find all loops; setup
variables as the unknown mesh currents;
apply KVL to each loop; solve for the
unknown voltages.
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Resistive Circuits – Analysis
Questions
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Using mesh current analysis, determine
the current through RL if Vsource = 5V,
R1=R2=10 KΩ, R3=R4=5 KΩ,
R5=RL=2 KΩ ?
Resistive Circuits – Other topics
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Superposition – Method of analyzing circuits with
2 or more independent sources by examining
effects of each source by itself and then
combing the effects.
Thevenin’s Theorem: A 2 terminal circuit can be
reduced to a voltage source in series with an
equivalent resistance.
Norton’s Theorem: A 2 terminal circuit can be
reduced to a current source in parallel with an
equivalent resistance.
Resistive Circuits – Other Topics
Questions
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Find the Thevenin equivalent with respect
to the 3K resistor.
Capacitors
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Capacitor – Device that stores charge.
Physically, 2 conductive plates that are very
close to each other but not touching
Capacitance: C = Q / V
Current through a capacitor: I = C (dv / dt)
Series capacitors: Ceq = (C1C2) / (C1 + C2)
Parallel capacitors : Ceq = (C1 + C2)
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Just the opposite of resistors
Acts like an open circuit to dc.
Inductors
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Device that stores energy in its magnetic field.
Resists changes in current by inducing a voltage
to oppose the change in current.
Physically: Coil of wire wrapped around a
conductive material.
Voltage through an inductor: v = L (di / dt)
Series and Parallel Inductors: Like resistors.
Acts like a short circuit to dc.
Capacitor/Inductor Questions
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What’s the equivalent capacitance of the
circuit below?
Combinations of Resistors,
Inductors, and Capacitors
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What is the step response of the circuit
below?
OP Amps
Takes an input and produces a desired
output.
 OP Amp – Can be designed to perform
mathematical operations such as addition,
subtraction, multiplication, division,
differentiation, and integration.
 Basis for analog computers
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OP Amp Questions
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What is Vo equal to in the circuit below?
AC Circuits Introduction
Sine waves, frequency, period
 RMS values of voltage
 Angular measurement of sine waves
 Equation for sine waves
 Non sinusoidal waveforms
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