Ohm's Law (2.1) Kirchhoff's Laws (2.2) - PowerPoint PPT Presentation

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Ohm's Law (2.1) Kirchhoff's Laws (2.2)

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Analogy: mass flow at pipe junction. i1(t) i2(t) i4(t) i5(t) i3(t) ... Analogy: pressure drop thru pipe loop. v1(t) v2(t) v3(t) lecture2. 13. KVL Polarity ... – PowerPoint PPT presentation

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Title: Ohm's Law (2.1) Kirchhoff's Laws (2.2)


1
Ohm's Law (2.1)Kirchhoff's Laws (2.2)
  • Prof. Phillips
  • January 24, 2003

2
Resistors
  • A resistor is a circuit element that dissipates
    electrical energy (usually as heat)
  • Real-world devices that are modeled by resistors
    incandescent light bulbs, heating elements
    (stoves, heaters, etc.), long wires
  • Resistance is measured in Ohms (W)

3
Ohms Law
  • v(t) i(t) R - or - V I R
  • p(t) i(t)v(t) i2(t) R v2(t)/R
  • Always dissipating or absorbing power (pgt0)

4
Example a 25W Bulb
  • If the voltage across a 25W bulb is 120V, what is
    its resistance?
  • R V2/P (120V)2/25W 576 ?
  • What is the current flowing through the 25W bulb?
  • I V/R 120V/576 ? 0.208 A 208 mA

5
Thought Question
  • When I measured the resistance of a 25W bulb, I
    got a value of about 40W. Whats wrong here?
  • Answer The resistance of a wire increases as
    the temperature increases. For tungsten, the
    temperature coefficient of resistivity is
    4.5x10-3/oK. A light bulb operates at about
    5000oF.

6
Open Circuit
  • What if R??
  • i(t) v(t)/R 0

7
Short Circuit
  • What if R0?
  • v(t) i(t) R 0

8
Class Example
9
Kirchhoffs Laws
  • Kirchhoffs Current Law (KCL)
  • sum of all currents entering a node is zero
  • sum of currents entering node is equal to sum of
    currents leaving node
  • Kirchhoffs Voltage Law (KVL)
  • sum of voltage (drops) around any loop in a
    circuit is zero

10
KCL (Kirchhoffs Current Law)
i1(t)
i5(t)
i2(t)
i4(t)
i3(t)
  • The sum of currents entering the node is zero
  • Analogy mass flow at pipe junction

11
Class Examples
12
KVL (Kirchhoffs Voltage Law)



v2(t)

v1(t)
v3(t)
  • The sum of voltages around a loop is zero
  • Analogy pressure drop thru pipe loop

13
KVL Polarity
  • A loop is any closed path through a circuit in
    which no node is encountered more than once
  • Voltage Polarity Convention
  • A voltage encountered to - is positive
  • A voltage encountered - to is negative

14
Class Examples
15
Electrical Analogies (Physical)
16
EE Subdisciplines
  • Communication/Signal Processing
  • Controls
  • Electronic Circuits
  • Electromagnetics
  • Power
  • Solid State

17
Power
  • Generation of electrical energy
  • Storage of electrical energy
  • Distribution of electrical energy
  • Rotating machinery-generators, motors

18
Electromagnetics
  • Propagation of electromagnetic energy
  • Antennas
  • Very high frequency signals
  • Fiber optics

19
Communications/Signal Proc.
  • Transmission of information electrically and
    optically
  • Modification of signals
  • enhancement
  • compression
  • noise reduction
  • filtering

20
Controls
  • Changing system inputs to obtain desired outputs
  • Feedback
  • Stability

21
Solid State
  • Devices
  • Transistors
  • Diodes (LEDs, Laser diodes)
  • Photodetectors
  • Miniaturization of electrical devices
  • Integration of many devices on a single chip

22
Digital
  • Digital (ones and zeros) signals and hardware
  • Computer architectures
  • Embedded computer systems
  • Microprocessors
  • Microcontrollers
  • DSP chips

23
Personal Systems Scaling
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