Quiz Preparation Have Quiz sheet ready l Top

Quiz Preparation Have Quiz sheet ready. l Top Center: QUIZ 3 l Upper Right: » Name (L, F, MI), » Today’s date 9/4/12 » Lab day , time » section number l Lab Day/Time Mon. 1: 00 Mon. 3: 00 Tue. 2: 00 Wed. 1: 00 Wed. 3: 00 Fri. Thu. 1: 00 2: 00 Thu. 2: 00 Fri. 1: 00 Section Number 8 9 36 10 10 11 11 12 29 35 12 12 1

Announcements l Read Chapter 6 before lab. l Work problems at the end of the Chapter 6 for practice. Solutions on web site. l Be sure to do the Pre-Lab assignment. You will lose in-lab points if you do not have the pre-lab worked when you arrive at lab. 2

Electricity – Water Analogy l Electricity flows through a circuit like water through a pipe. » charge -- # of water molecules in the pipe » current -- water flow rate (gallons per minute) » voltage – pressure (psi = pounds per square inch) » resistance -- resistance to flow (inverse of pipe cross-sectional area) » capacitance -- water stored under pressure (e. g. a bladder tank) 3

Units charge -- coulombs (C) l current -- amperes (A), A=C/s l voltage -- volts (V) l resistance -- ohms ( ), =V/A l capacitance -- farads (F), F = C/V Note: Farads are huge units -- usually use F (microfarads) l 4

Circuit Elements l voltage source (e. g. battery) – like water pump with specified pressure. Units: volts (V) 5

Circuit Elements l resistor -- pipe with small cross-sectional area that impedes water flow. Units: ohms ( ) Wire can be viewed as a resistor with very low or zero resistance. 6

Circuit Elements l CAPACITOR – a reservoir or sponge that can store water (charge). Units of capacitance: Farads (F) 7

Circuit Elements l diode -- valve that only allows current flow one direction. (No units) current 8

Quiz l 1. Electric current is analogous to: » a. water pressure » b. water flow rate » c. # of water molecules in the pipe l 2. Voltage is analogous to: » a. water pressure » b. water flow rate » c. # of water molecules in the pipe 9

Ohm’s Law l The current I flowing through a resistor is proportional to the voltage V across it and inversely proportional to the resistance R: or 10

Ohm’s Law - Example I 100 + 5 V - Always: ·Label current directions ·Put +/- signs on voltages I = 5/100 = 0. 05 A Passive sign convention: place the positive voltage reference at the same terminal that the current enters 11

Quiz 3. The current I is (a) 100 A (b) 0. 01 A (c) -10, 000 A I 1000 + 10 V - 12

Connection Types l Series (daisy chain) l Parallel (side by side) 13

Series Connection l Single branch. Current is the same through all elements. I 14

Series Connection l Resistors add in series. Ex: R 1=50 , R 2=100 R=150 15

Multiple Voltage Sources l Multiple voltage sources in series add. l These circuits are equivalent. 16

Wait – I thought they ADDED! 10 + 4 = 6? l Have to look at the polarity l + 10 - 1 k 4 + 17

Parallel Connection l Multiple branches connected at both ends. The voltage is the same across all elements. 18

Parallel Connection l The reciprocal of resistance adds. » For two resistors only = product / sum Ex: R 1=50 , R 2=100 R=(50)(100)/150=33. 33 19

Series vs. Parallel l. Are the lights in your house/apartment wired in series or parallel? Answer: Parallel! 20

Voltage Division (wire) (motor) • If R 1 represents the wire resistance and R 2 represents the motor and motor circuit resistance, we want R 1 to be as small as possible. This will deliver the maximum voltage to the motor. 21

Voltage Division - Example 10 15 V 20 22

Resistors in Parallel - Example I 1 I 2 Vo l What is the current in each branch? 23

Resistors in Parallel - Example I 1 I 2 Vo l Voltage is the same across each branch– use Ohm’s law: 24

Resistors in Parallel - Example I 1 Vo 15 V l I 2 10 20 Ohm’s law 25

Series/Parallel Example I 1 l I 2 What is the current in each branch? 26

Series/Parallel Example I 1 I 2 2 k l Combine the two 1 kΩ resistors in series. 27

Diode Example + VR Vo l R I What is the current in the circuit (I) and the voltage drop across the resistor (VR)? 28

Diode Example + VR Vo R I VD=0. 7 V 29

Diode Example + VR 9 V 1 k I VD=0. 7 V 30

Breadboards l Used for rapid prototyping » Easier & faster than soldering » Allow for easy alterations Generally for temporary use l Components just plug in l 31

How a Breadboard Works Connect components by plugging them in l Components are connected by copper wires underneath holes l 32

Connecting Resistors in Series 33

Connecting Resistors in Parallel 34

Quiz 4. Voltage division is used (a) to find the voltage across a single element in a series circuit (b) to find the voltage across a single branch in a parallel circuit (c) to determine the fair allocation of batteries in a team-based design 35

Quiz 5. Current division is used (a) to find the current through a single element in a series circuit (b) to find the current through a single branch in a parallel circuit (c) to determine the fair allocation of batteries in a team-based design 36