Chapter 1wup

Chapter 1: The Analysis and
Design of Linear Circuits
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Circuit Analysis I
You’ll learn these tools in all subsequent
classes
Definitions

Definitions
Circuit – interconnected electrical
devices that carry electrical energy and
information
Circuit diagram – a model of the real
thing that helps us write equations to
predict electrical behavior of the real
circuit.

Assumptions for circuit model
Electrical effects occur instantaneously
throughout the circuit
Net charge on every element is zero
First law of thermodynamics holds
(energy is conserved)
Problem solving
• Words pictures equations solutions
pictures words & check

Know these!

Water Analogy

Know and Use Engineering notation
1000V=? V, kV
.0034A=? A, mA
.0763 mW=?, W, μW
Form: aaa x 10 b units = aaa (prefix units) where aaa
varies from 0.aaa to aaa, b is divisible by 3.

Circuit Variables: i, v, p
Current, net flow of charge per unit
time
• i=dq/dt – current
(Amperes=coulombs/sec)
• q – charge, coulombs
• t – time, sec
• Current direction is the direction positive
charge would flow through an element

Circuit Variables: i, v, p
Voltage – the change in energy from
one point to another.
• Voltage is relative and is measured across
an element.
• v=dw/dq
• v= voltage (joules/coulomb)
• w= energy, joules
• q= charge, coulombs

Circuit Variables: i, v, p
Power
• Power is the rate of energy transfer
• P=dw/dt
• P= power, watts
• w=energy in joules
• t=time
• Power is absorbed from the circuit by an element or
delivered to the circuit by an element.
• Because energy is conserved for the circuit. All the energy
is delivered to the circuit is absorbed by the other elements
in the circuit.
• p=iv for any element
• p=i 2 R=v 2 /R (for a resister only)

Water Analogy

Sign Convention
You must label the elements in a circuit
to calculate current, voltage, or power
for an element. Labeling is our choice.
(passive)
• This is the standard way to label elements.

Special Case for Sources
Sources can be labeled either passive
(book method) or active (Tom’s way).
If power is positive, the element is
absorbing power from the circuit.
If power is negative the element is
delivering power to the circuit.

Battery example

Figure 1-5, Example 1-3, pg 9

High Amperage
The unit of electric current is ampere,
and the electric current is often loosely
called amperage. Can there exist a
situation where there is a lot of
amperage without also having a lot of
voltage at the same time?

High Resistance
Most of the resistance in this circuit is
in the
a) wire cord
b) light bulb