ENGG1030 Electrical Physics and Electronics · ENG1030 Electrical Physics and Electronics B.Lovell/T.Downs School of Computer Science and Electrical Engineering 9 23/03/01 Lecture

ENG1030 Electrical Physics and Electronics B.Lovell/T.Downs

School of Computer Science and Electrical Engineering

1

23/03/01

Lecture 1

ENGG1030 Electrical Physics and Electronics

School of CSEEThe University of Queensland



2

23/03/01

Lecture 1

Course Outline

• The lecture course is divided into three parts of about 6 hrs– Electrical Circuits– Electronics – Digital Circuits

• There are three laboratory sessions in three different laboratories which may occur in any order– Digital Circuits (Computer Systems Lab 47-405)– LC AM Radio (Electronics Lab 47-501)– Induction Motor (Machines Lab 50-S106)



3

23/03/01

Lecture 1

Course Outline

• Extensive use will be made of the website www.csee.uq.edu.au/~engg1030

in delivery of this course• The following information will be posted as available

– Lecture notes– Software and demonstration scripts– Tutorial assignments– Laboratory instruction sheets and schedules– Notices and Announcements– Marks for continuous assessment



4

23/03/01

Lecture 1

Electrical Circuits



5

23/03/01

Lecture 1

Electrical Concepts

• Fundamental Concepts– An Electrical Circuit

• An electrical circuit is simply a collection of electrical devices and the wires connecting them. Usually circuits are drawn in a schematic form which helps in understanding the behaviour of the circuit. This is called a schematic diagram.

• Sometimes we are more interested in the physical layout of the wiring. For example, in a car we are often more interested in the colour coding of the wires and the physical location of the wires in the vehicle. In this case, we might use a wiring diagramor perhaps a harness diagram. These diagrams are very useful for maintenance and assembly.

• Since engineers are concerned with design issues, we will concentrate on schematic diagrams.



6

23/03/01

Lecture 1

Flashlight Example

Circuit modeling for a two-cell flashlight. The complex physical deviceis reduced to a simple electrical circuit using standard symbols andsimplifying assumptions about how they work.



7

23/03/01

Lecture 1

Wiring Diagram for Car



8

23/03/01

Lecture 1

Harness Diagram for Car



9

23/03/01

Lecture 1

Comments

• The battery circuit is a simple example of direct current (DC)

• The electrical power from plug sockets in the home is supplied in AC (alternating current) form. The voltage driving the current flow is a sinusoid at 50Hz and 240V(rms).

• For the moment we will concern ourselves with dc circuits since these are generally simpler

• However, most of the principles of DC circuit analysis are readily extended to AC circuits



10

23/03/01

Lecture 1

0 1 0 2 0 30 4 0 5 0 60 7 0-400

-300

-200

-100

0

1 0 0

2 0 0

3 0 0

4 0 0

Time (ms)

Vol

ts

Mains AC Voltage Waveform

240 VAC

Same heatingeffect as 240V DC

340 VPeak

Measuredbetween activeandneutrallinesA N

E



11

23/03/01

Lecture 1

Basic Concepts

• Since electrical quantities such as voltage and current cannot be directly observed with our human senses, students often exhibit some confusion with these concepts.

• A common way to explain the workings of many devices is to draw an analogy between the flow of electricity and the flow of water.

• In this model, we can consider an electrical current in a wire, which is the flow of electrons through the wire, to be similar to the flow of water in a pipe.



12

23/03/01

Lecture 1

Current and Voltage

• In both cases we measure current in terms of rate of flow.

• For water, we could measure the current in terms of the number of molecules passing a given point per second. – This would yield very large numbers in practical applications– The solution is to use more convenient units such as

litres/per second.



13

23/03/01

Lecture 1

Current and Voltage

• For electricity, we could measure the current in terms of the number of electrons passing a given point per second. – Similarly, this would yield very large numbers in practical

applications– The solution is to use a more convenient unit for electrical

charge — a Coulomb– A Coulomb is an electric charge equal to 6.3x1018 electrons– A flow rate of electric charge of one Coulomb per second is,

by definition, equal to a current of one Ampere.– The symbol for the Ampere is A.



14

23/03/01

Lecture 1

SI Units

• The Ampere and the Coulomb belong the the internationally agreed set of units called the SI system which is universally employed in EE.

• All measurements are expressed in terms of combinations of the 5 basic dimensions– length, mass, time, temperature, current, luminous intensity

• This helps explain why the Coulomb is a weird number– It was defined before the charge on the electron could be

measured (Millikan oil drop experiment 1923); Indeed, it was defined before the electron was discovered.



15

23/03/01

Lecture 1

SI Units

Quantity Symbol Unit Abbrev

Length l meter m

Mass m kilogram kg

Time t Second s

Temperature τ Kelvin K

Current i Ampere A

LuminousIntensity

I Candela cd



16

23/03/01

Lecture 1

Electrical Current

• One Ampere (or Amp, for short) is quite is large current in an electronic device or computer

• In these application areas we are often dealing with much smaller currents and talk in terms of milliamps (mA), microamps (µA), or even nanoamps (nA).

• For example, the current in the flashlight example given earlier would be 0.25A or 250mA.

• In engineering, we use the SI prefixes milli-, micro-, and nano- etc to scale somewhat inconvenient standard units to convenient sizes.



17

23/03/01

Lecture 1

SI Prefixes

Prefix Abbrev ScalingTera T 1012

Giga G 109

Mega M 106

kilo k 103

(none) 100

milli m 10-3

micro µ 10-6

nano n 10-9

pico p 10-12



18

23/03/01

Lecture 1

Symbols

• We often use the symbol, I or i, to denote a current in a circuit and Q or q to denote a charge.

• We can use subscripts to distinguish between, say, multiple currents in a circuit. For example, I1, I2, and I3.

• These symbols can be used to express the fact that current is the rate of flow of charge as follows:

Here i(t) denotes the instantaneous current flowing

∫==T

dttiQdtdQ

I0

)(lyequivalentor

Documents

ENGG1030 Electrical Physics and Electronics · ENG1030 Electrical Physics and Electronics B.Lovell/T.Downs School of Computer Science and Electrical Engineering 9 23/03/01 Lecture