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# ENGG1015 Tutorial 1

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### ENGG1015 Tutorial 1

1. 1. ENGG 1015 Tutorial Introduction to Electrical and Electronic Engineering – 2011 Fall Semester Time and Venue Class A: 1300-1355 MB201 Class B: 1130-1225 CYC-C Tutor Leon LEI (me): CYC806, engg1015-staff@eee.hku.hk Tutorial materials http://www.eee.hku.hk/~culei/ENGG1015.html 1
2. 2. ENGG 1015 Tutorial Each class: 40 min. tutorial + 15 min. Q/A Allow “no/low” voice discussion Go outside for phone conversations Same contents for Class A and Class B Tutorial materials Regular tutorials Revision tutorial before examination (Tentatively) Question bank Solutions and Exemplars of last year homework Extra MCQs, Extra SQs No homework plagiarism 2
3. 3. ENGG 1015 Tutorial Formats of tutorial materials Slides Handout Problem sets 3
4. 4. ENGG 1015 Tutorial Facebook page “ENGG1015 FA11” Class news, photos, videos RSS feed “Like”! RSS feed 4
5. 5. ENGG 1015 Tutorial Circuits (I) (Class A) 12 Sept and (Class B) 6 Sept Learning Objectives Identify basic electrical components (Voltage, Current, Resistance) and electrical rules News Lab/Project preparation Ack.: MIT OCW 6.01 and 8.02 5
6. 6. What is a Circuit? Circuits are connects of components Through which currents flow Across which voltages develop 6
7. 7. 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) 7
8. 8. Rules Governing Flow Rule 2: Like the flow of water, the flow of electrical current (charged particles) is incompressible Node Kirchoff’s Current Law (KCL): the sum of the currents into a node is zero 8
9. 9. Rules Governing Voltages Voltages accumulate in loops Kirchoff’s Voltage Law (KVL): the sum of the voltages around a closed loop is zero 9
10. 10. Parallel Connection and Series Connection 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 Series connection 10
11. 11. Electrical Symbols Voltage source Resistor Switch Often connected in series When the switch is open the load is disconnected When the switch is closed, the load is connected 11
12. 12. Power Supply http://ocw.mit.edu/courses/physics/8-02- electricity-and-magnetism-spring-2002/video- lectures/lecture-10-batteries-and-emf/ or http://www.youtube.com/watch?v=RQX8I9Z WtPQ Definition and explanation of a battery 4:11 minutes (0:00 - 4:11) Symbol for a battery in a circuit diagram Definition of internal resistance 3:34 minutes (7:16 - 10:50) 12
13. 13. Measuring Voltage A voltmeter must be hooked in parallel across the element you want to measure the voltage across Voltmeters have a very large resistance They don’t affect the circuit too much 13
14. 14. Measuring Current An ammeter must be hooked in series with the element you want to measure the current through Ammeters have a very low resistance They don’t affect the circuit too much 14
15. 15. Resistors and Ohm’s Law Length Cross-section area Series connection Parallel connection 15
16. 16. Resistance of Wires Wires are made from conductors that have resistance Include a series resistor to model the wire resistance Rw The current into a resistor is given by I= V/Req = V/(R+Rw1+Rw2) In practice, we will make the wire resistance much smaller than the component resistance: R >> Rw 16
17. 17. Measuring Resistance An ohmmeter must be hooked in parallel across the element you want to measure the resistance Ohmmeters apply a voltage and measure the current that flows They typically won’t work if the resistor is powered (connected to a battery) Measuring R1 17
18. 18. Internal Resistance 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 a resistant r inside the battery Maximum current the battery can generate: Imax=V/r 18
19. 19. Demonstration: Batteries in Series http://ocw.mit.edu/courses/physics/8-02- electricity-and-magnetism-spring-2002/video- lectures/lecture-10-batteries-and-emf/ or http://www.youtube.com/watch?v=RQX8I9Z WtPQ Connecting two batteries in series 4:30 minutes (10:50 - 15:20) 19
20. 20. Quick Checking Resistors and Ohm’s Law Ohm’s Law is XXX Measure Voltage & Current An ammeter must be hooked in XXX Internal Resistance of Battery Equivalent circuit of a non-ideal battery is XXX 20
21. 21. Quick Checking Resistors and Ohm’s Law Ohm’s Law is “V=IR” Measure Voltage & Current An ammeter must be hooked in series Internal Resistance of Battery Equivalent circuit of a non-ideal battery is 21