corriente continua

DC Circuits

Chapter 1

CHAPTER 1. DC CIRCUITS
1.1 1.2 1.3 1.4 1.5 1.6 -

Fundamental magnitudes
Elements of a circuit
Ohm’s and Joule’s Laws
Kirchoff’s Laws
Nodal and mesh analysis
Equivalent circuits
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Chapter 1

Lecture 1

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Chapter 1

1.1. Fundamental magnitudes

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Chapter 1

IS conventional prefixes
10-12
101210-9

10-6

10-3

pico(p) nano(n) micro(μ) milli(m)

1

103

106

109

kilo(k) mega(M) giga(G) tera(T)

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Chapter 1

Current, voltage and power
• Basic magnitudes: current, voltage and
power:
– Current: measure of the amount of electrical
charge transferred per unit time: I = dq/dt
1 A = 1 C/s

– Voltage: Electromotive force or potential, V
1 V = 1J/C = 1 N·m/C

– Power: P = I · V
1 W = 1 V·A = 1 J/s
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Current, I
• Conventionally, the current has been related to the
movement of positive charges, although in reality
the current is generated by the movement of
electrons (negative charges)
• The sign of the current indicates the sense of the
flux.
• It can be distinguished between:
– DC current(dc): invariant current throughout the time,
p.e.: bateries and especial generators.
– AC current (ac): current that changes throughout the time,
p.e.: a domestic electricity network.
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Voltage, V
• The voltage between two ends of a path is
the total energy required to move a small
electric charge along that path

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Signconvention
• Passive sign convention: the current enters by the
positive terminal of the voltage

• Consequence for P = I·V
– Positive power(+): the element absorbs power.
– Negative power(-): the element delivers power.
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Example
• Example exercise E1.1: Determine the
power absorbed or delivered by the
following elements:
+
12V
I=4A

V1 = 12V

(a)Solution: P = -48 W

Solution: P = 8 W
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Example
• Example exercise E1.2: Find the unknown
variables in the following circuits:

Solution: V1 = -20 V

Solution: I = -5 A
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Chapter 1

1.2. Elements of a circuit

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Elements of a circuit
• The Active Elements generate energy:
– Bateries.
– Voltage orcurrent sources.

• The Passive Elements do not generate
energy:
– Resistors.
– Capacitive or inductive elements (do not
generate but store energy).
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Dependent and Independent Sources
- An independent source (either voltage or current)
does not depend on the value of other voltage or current
sources in the circuit.

Independent voltage sourceIndependent current source

- The magnitude of the voltage or the current in a
dependent source is a function of other magnitudes of
the circuit.
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Example
• Example exercise E1.3: Find the power
absorbed or delivered at each element of the
following circuit:
Solución:
P12V = -36 W
P1 = 54 W
P2 = -18 W

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Dependent voltagesources
6Vx

Voltage
controlled
voltage source

6000Ix

Current
controlled
voltage source

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Chapter 1

Dependent current sources

Voltage
controlled current
source

Current
controlled current
source

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Chapter 1

Dependent Sources

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Example
• Example exercice E1.4(a): Determine
the power suppliedby the dependent
source of the following circuit:

Solution: P = -80 W
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Chapter 1

Example
• Example exercise E1.5: Determine
the power supplied or absorbed by the
elements of the following circuit:
Solution:
P24V = -96 W
P1 = 32 W
P4Ix = 64 W

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Chapter 1

1.3. Ohm’s and Joule’s Laws

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Resistor
• A...