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ENGG 1015 Tutorial

Introduction to Electrical and Electronic Engineering – 2011 Fall SemesterTime and Venue

Class A: 1300-1355 MB201Class B: 1130-1225 CYC-C

TutorLeon LEI (me): CYC806, engg1015-staff@eee.hku.hk

Tutorial materialshttp://www.eee.hku.hk/~culei/ENGG1015.html

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ENGG 1015 Tutorial

Each class: 40 min. tutorial + 15 min. Q/AAllow “no/low” voice discussionGo outside for phone conversationsSame contents for Class A and Class B

Tutorial materialsRegular tutorialsRevision tutorial before examination (Tentatively)Question bank

Solutions and Exemplars of last year homeworkExtra MCQs, Extra SQs

No homework plagiarism

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Formats of tutorial materialsSlidesHandoutProblem sets

ENGG 1015 Tutorial

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ENGG 1015 Tutorial

Facebook page“ENGG1015 FA11”Class news, photos, videosRSS feed“Like”!

RSS feed

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ENGG 1015 Tutorial

Circuits (I)(Class A) 12 Sept and (Class B) 6 SeptLearning Objectives

Identify basic electrical components (Voltage, Current, Resistance) and electrical rules

NewsLab/Project preparation

Ack.: MIT OCW 6.01 and 8.02

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What is a Circuit?

Circuits are connects of componentsThrough which currents flowAcross which voltages develop

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Rules Governing Flow

Rule 1: Currents flow in loops

The same amount of current flows into the bulb (top path) and out of the bulb (bottom path)

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Rules Governing Flow

Rule 2: Like the flow of water, the flow of electrical current (charged particles) is incompressible

Kirchoff’s Current Law (KCL): the sum of the currents into a node is zero

Node

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Rules Governing Voltages

Voltages accumulate in loops

Kirchoff’s Voltage Law (KVL): the sum of the voltages around a closed loop is zero

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Loads are connected in parallel across power supply.When the elements are connected one after another, so that the current passes through each element without any branches, the elements are in series.

Parallel Connection and Series Connection

Parallel connection Series connection

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Voltage source

Resistor

SwitchOften connected in seriesWhen the switch is open the load is disconnectedWhen the switch is closed, the load is connected

Electrical Symbols

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http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/lecture-10-batteries-and-emf/ orhttp://www.youtube.com/watch?v=RQX8I9ZWtPQDefinition and explanation of a battery

4:11 minutes (0:00 - 4:11)Symbol for a battery in a circuit diagram

Definition of internal resistance3:34 minutes (7:16 - 10:50)

Power Supply

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A voltmeter must be hooked in parallelacross the element you want to measure the voltage acrossVoltmeters have a very largeresistance

They don’t affect the circuittoo much

Measuring Voltage

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An ammeter must be hooked in series with the element you want to measure the current throughAmmeters have a very lowresistance

They don’t affect the circuittoo much

Measuring Current

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Resistors and Ohm’s Law

Series connection Parallel connection

Length

Cross-section area

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Wires are made from conductorsthat have resistance

Include a series resistor tomodel the wire resistance Rw

The current into a resistor is given byI= V/Req = V/(R+Rw1+Rw2)In practice, we will make the wire resistance much smaller than the component resistance: R >> Rw

Resistance of Wires

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Measuring Resistance

An ohmmeter must be hooked in parallelacross the element you want to measure the resistanceOhmmeters apply a voltage and measure the current that flowsThey typically won’t workif the resistor is powered(connected to a battery)

Measuring R1

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When battery delivers current to circuit, there is a flow of current in the battery itself.The chemical reaction will dissipate energy

Battery goes hot Lost energy in the circuit

Equivalent to having aresistant r inside the battery

Maximum current the battery can generate: Imax=V/r

Internal Resistance

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http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/lecture-10-batteries-and-emf/ orhttp://www.youtube.com/watch?v=RQX8I9ZWtPQConnecting two batteries in series

4:30 minutes (10:50 - 15:20)

Demonstration: Batteries in Series

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Resistors and Ohm’s LawOhm’s Law is XXX

Measure Voltage & CurrentAn ammeter must be hooked in XXX

Internal Resistance of BatteryEquivalent circuit of a non-ideal battery is XXX

Quick Checking

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Quick Checking

Resistors and Ohm’s LawOhm’s Law is “V=IR”

Measure Voltage & CurrentAn ammeter must be hooked in series

Internal Resistance of BatteryEquivalent circuit of a non-ideal battery is