Circuits Chapter 1

8/7/2019 Circuits Chapter 1

1/102

1.1 OVERVIEW OF ELECTRICAL

ENGINEERINGElectrical Engineering:

a) Collect, Store, Process, Transport, and

Present Information

b) Distribute, Store and Convert Energy betweenvarious forms.

Manipulation of Information

Manipulation of Energy.


2/102

Example

Weather PredictionData collected by weather satellites, land based

radar stations, and sensors at numerous weatherstations.

Sensors: Devices that convert physicalmeasurements to electrical signals.

Information is then transmitted by electroniccommunication systems and processed by

computers to yield forecasts.Forecasts are electronically displayed.


3/102

Example 2

Electrical Power PlantsEnergy is converted from various forms to

electrical form.Electrical distribution systems transport the energy

to our homes, factories, businesses.


4/102

Applications of Electrical

Engineering

Many ApplicationsAutomakers use electrical technology to provide

increase functionality at lower costs. Theseinclude:


5/102


6/102

Subdivisions of Electrical

Engineering

1) COMMUNICATION SYSTEMS:Transport information in electrical form.

Cell Phones, Satellite TV's, Internet

2) COMPUTER SYSTEMS:Process and store information in digital form.PC's, Computers used in auto's, homes, etc.


7/102

3) CONTROL SYSTEMS:Collect information w/ sensors and use electrical

energy to control a physical process.Heating/Cooling Systems: Thermostat (sensors)

measures current temperature and compares it w/desired value. Control circuits operate the furnace orthe air conditioner to achieve the desired temperature.

Tall buildings have control systems installed to reducethe movement by wind.

Feedback is important!


8/102


9/102

5) ELECTRONICS

Study and applications of materials, devices andcircuits used in amplifying and switching electrical

signals.

Transistors: used everywhere electricalinformation or energy is employed.

Cardiac Pacemaker: Senses heart beats, if nobeat, then applies a minute of electrical stimulusto the heart, forcing the heart to beat.


10/102

6) PHOTONICS

New Field: promises to replace conventionalcomputing, signal processing, sensing andcommunications devices.

Previous are all based on manipulating electrons.

PHOTONICS is based on manipulating photons.Light generation by lasers and light emittingdiodes, transmission of light through optical

components.

Readers for DVDs, holograms, optical signalprocessors, Fiber optic communication systems.

Future Optical Computers, HolographicMemories, Medical Devices.


11/102

7) POWER SYSTEMS

Convert energy to and from electrical formTransport energy over long distancesComposed of generators, transformers and

distribution lines, motors, etc.


12/102

8) SIGNAL PROCESSING

Used to extract useful information from electricalsignals derived from sensors

Machine vision for robots.


13/102

WHYSTUDY ELECTRICAL ENGINEERING?

1) To pass the Fundamentals of Engineering(FE) exam as a 1st step in becoming a registered

Professional Engineer.

2) To have a broad knowledge base so you can

lead design projects in your own field

3) Ability to operate and maintain electricalsystems, such as those found in control systems

for manufacturing processes.

4) Ability to communicate with ElectricalEngineering Consultants.


14/102

SECTION 1.2

CIRCUITS, CURRENTS,VOLTAGES


15/102

Figure 1.2 The headlight circuit. (a) The actual physical layout of the circuit. (b) The circuit diagram.


16/102

Chemical forces in the battery cause the electricalcharge (electrons) to flow through the circuit.

Energy is gained from the chemicals in the batteryand delivered to the headlights.

Transported through an excellent electricalconductor(copper wire), that are insulated.Switch is used to control the flow of the current.

When the switch is closed (shorted), current flows,when it is open, the current does not flow.

Headlamps contain tungsten wires they canwithstand high temperatures. They do not

conduct electricity (they resist)


17/102

When electrons collide with the atoms of thetungsten wires, heat is released.

Thus a chemical action in the battery istransformed by the electrons through insulatedwires to the tungsten, where electrons are resisted

and heat occurs.

Tungsten becomes hot so light is emitted.


18/102

FLUID FLOW Analogy

Electrical Circuits are similar to fluid flow systems.

Battery --- PumpCharge ----- FluidConductors ---- Frictionless pipes

Current ---- Rate of Flow of the Fluid

Voltage --- Pressure differentialSwitches --- Valves


19/102

Electrical Circuits:

Electrical circuits consist of various circuitelements (CE) connected in a closed path by

conductors.

Circuit elements can beVoltage sources

ResistancesInductances

Capacitances


20/102


21/102

Electrical Current:

Is the time rate of flow of electrical charge through

a conductor or circuit element.

Units: Amperes (A)==> Coulombs / second (c/s)

Charge on an electron: -1.602x10^-19 C


22/102


23/102

We take the cross section of a circuit elementperpendicular to the flow of the current. Then we

select a REFERENCE DIRECTION along thedirection of the flow.

The electrical current following in the REF. DIR. Is

given by:

i(t) = dq(t)/dt.

A current of 1 Ampere means that one coulomb ofcharge passes through the cross section each

second.


24/102

To find the charge, we integrate the current.


25/102


26/102


27/102

REFERENCE DIRECTIONS:

In analyzing electrical circuits, we may not initially

know the actual direction of the current flow.We start by assigning current variables and weselect an arbitrary direction for each current of

interest.


28/102


29/102

Direct Current and Alternating Current

Direct Current (DC) --- Constant w/ timeAlternating Current (AC), Varies w/ time,

magnitude and direction may change periodically.


30/102


31/102


32/102

Double Subscript Notation for Currents


33/102


34/102

Ex: A constant current of4A flows through a CE.In 10 Sec, how much net charge passes through

the CE?

Solution:


35/102

Example

q(t) = 0.01 sin(200t), determine i(t).

Solution:

i(t) = d/dt q(t) = d/dt (.01sin(200t))

= 2 cos (200t) A.


36/102

Voltages:

When charges move through a CE, energy istranferred.

In the case of the automobile headlights, energy is

supplied by the chemicals in the battery and isabsorbed by the headlights as heat and light.

Voltage ==> Energy transferred per unit of

charge.

Units: V = J/C


37/102


38/102


39/102


40/102

Switches:

Control the flow of currents in a circuit.When an ideal switch is open, no current will flow

through it and the voltage is determined by theother elements in the circuit.When an ideal switch is closed, (we call it short

circuit), the voltage across it is zero, and the

current through it is determined by the otherelements in the circuit.


41/102

Assigning Arbitrary values for voltages:

When we are analyzing circuits, if we do not knowthe voltage variables, we can start by choosing

reference polarities arbitrarily.


42/102


43/102

Figure 1.12 The voltage vab has a referencepolarity that is positive at point a and negative at

point b.


44/102

Figure 1.13 The positive reference forv is at the

head of the arrow.


45/102

Example: Vab

= 20V, A positive charge of 2Cmoves through the CE from b to a.

Find the energy transferred.

+

--

a

b

2C

E = 20 V x -2 C

= 20 (J/C) x -2 C

= -40 J Supplied By the CE


46/102

Section 1.3

Power and Energy


47/102

P = V I Volts x Amperes(J/C) x (C/s)

(J/s) == > Watts !!!

Power = Rate of Energy Transfer


48/102

Positive Reference Configuration:

If P is positive, Energy is being absorbed by the

CE

If P is Negative, Energy is being supplied by theCE.


49/102

Figure 1.14 When current flows through anelement and voltage appears across the element,

energy is transferred. The rate of energy transferis p = vi.


50/102


51/102


52/102


53/102


54/102

Energy Calculations:


55/102


56/102

Section 1.4

Kirchhoff's Current Law


57/102

Node: A point in an electrical circuit where two ormore Ces are joined together.

Kirchhoff's Current Law (KCL):The net current entering a node is zero.


58/102

i1

+ i2- i

3= 0

i3 - i4= 0i5

+ i6

+ i7

=0


59/102

Note: All points in a circuit that are connected by

simple conducting wires (i.e. no CE), areconsidered to be a single node.


60/102


61/102


62/102


63/102


64/102

Section 1.5

Kirchhoff's Voltage Law


65/102


66/102


67/102

Kirchhoff's Voltage Law (KVL):

The algebraic sum of all the voltages equals zerofor any closed path (loop) in an electrical circuit.


68/102


69/102


70/102


71/102

Parallel Circuits:

Two circuit elements are parallel if both ends ofone element is connected directly to the

corresponding ends of the other element.


72/102


73/102


74/102


75/102


76/102

Section 1.6

Introduction to Circuit Elements


77/102


78/102

Conductors:

Conduct electricity (copper wires).Voltage across = 0 regardless of current thru it.

When two points are joined by an ideal conductor,we say the points are shorted together.

Ideal Conductor === Short Circuit


79/102

Independent Voltage Sources:

Maintain a specified voltage across its terminals.Voltage is independent of other voltages across

other CE's and the current thru it.


80/102


81/102


82/102

Dependent Voltage Sources:

Voltage across the source depends on the othervoltages or currents in the circuit.


83/102


84/102

Independent Current Sources:

Forces a specified current to flow through itself.This current value is independent of the voltage

across it or the currents flowing through the otherCE's.


85/102


86/102

Dependent Current Sources:

Forced current depends on the voltage or thecurrent across some other element in the circuit.


87/102


88/102

Resistors and Ohm's Law:

The voltage across an ideal resistor is proportionalto the current through the resistor.

The constant of proportionality is the resistance R.

Ohm's Law: v = I R

Units of R are ohms.


89/102


90/102


91/102


92/102


93/102


94/102


95/102


96/102


97/102

Ex: Compute the Resistance of a copper wirehaving a diameter of 2.05 mm and a length of

10m.


98/102


99/102


100/102


101/102


102/102

Circuits Chapter 1

Documents

Transcript of Circuits Chapter 1