© 2005 Baylor University EGR 1301 Slide 1 Lecture 21 Introduction to Engineering Approximate Running Time - 23 minutes Distance Learning / Online Instructional Presentation Presented by Department of Mechanical Engineering Baylor University Procedures: 1.Select “Slide Show” with the menu: Slide Show|View Show (F5 key), and hit “Enter” 2.You will hear “CHIMES” at the completion of the audio portion of each slide; hit the “Enter” key, or the “Page Down” key, or “Left Click” 3.You may exit the slide show at any time with the “Esc” key; and you may select and replay any slide, by navigating with the “Page Up/Down” keys, and then hitting “Shift+F5”.

© 2005 Baylor University EGR 1301 Slide 2 Lecture 21: Electrical Engineering Topic 1 Voltage and Current Professor Brian Thomas Speaking

© 2005 Baylor University EGR 1301 Slide 3 Outline Electrical Engineering: Information and Power Electricity Basics –Charge –Current, Voltage, –Power –AC, DC, grid power

© 2005 Baylor University EGR 1301 Slide 4 Information and Power Information –Radio –Television –Internet –Cellular telephone –Satellites –Embedded systems –Fiber optics, lasers Power –Lighting –Appliances –Motors –Heating –Welding & manufacturing –On grid / off grid –EMP

© 2005 Baylor University EGR 1301 Slide 5 Electricity Basics Charge –The smallest bit of charge is the charge of an electron –Charge flowing is called “Current” –Charge accumulated produces “Voltage”

© 2005 Baylor University EGR 1301 Slide 6 Electric Current “Free” electron Atom Electrons are free to flow in metals and other “conductors” Materials where charge may not flow are “insulators” An electron removed from a neutral atom leaves behind a “hole” By convention: electrons have negative charge, protons (and holes) have positive charge

© 2005 Baylor University EGR 1301 Slide 7 Electric Current 1 “Coulomb” of charge is 6,241,506,360,000,000,000 electrons If 1 Coulomb flows through a wire in 1 second, we say the current is 1 ampere or 1 “amp” Current always “flows through”

© 2005 Baylor University EGR 1301 Slide 8 Current Magnitudes Brain cell synaptic currents ( A) Integrated circuits currents (10 -4 A) Threshold of human sensation (10 -3 A) Causes Ventricular fibrillation (10 -1 A) Household appliances (10 A) Large Industrial Equipment (100 A) Lightning Bolt (1000 A)

© 2005 Baylor University EGR 1301 Slide 9 Electrostatic Forces Electrostatic force gives rise to stored energy Stored energy mental images –Stretched rubber bands –Compressed springs –Water pressure (or height of column of water)

© 2005 Baylor University EGR 1301 Slide 10 Electrostatic Force Example

© 2005 Baylor University EGR 1301 Slide 11 Voltage Voltage arises from accumulated charge being separated Opposite Charges Attract –Positive likes negative and visa versa –Energy is required to keep them apart Like the ends of a rubber band Rubber bands can be stretched to different lengths “Voltage” is a measure of how much energy each coulomb of charge contains

© 2005 Baylor University EGR 1301 Slide 12 1 “volt” means each coulomb of charge can release 1 Joule of energy A 12 Volt battery will produce 12 Joules of energy for every coulomb of electrons delivered Voltage 120 VAC

© 2005 Baylor University EGR 1301 Slide 13 Voltage exists between two points, not at an individual point The earth is a common reference point –“Ground” –Voltages with respect ground are like rubber bands with one end on the ground Voltage

© 2005 Baylor University EGR 1301 Slide 14 Power Power is the rate at which energy is transferred Electric Power is found by multiplying voltage and current

© 2005 Baylor University EGR 1301 Slide 15 Power Question: How much power is supplied to a belt sander that draws 15 amps using “wall” voltage? Answer: –120 Volts x 15 Amps = 1800 Watts 1800 W = 1.8 kW

© 2005 Baylor University EGR 1301 Slide 16 AC, DC, and all that DC stands for “direct current” and means the voltage and current are constant –All batteries supply DC power –“Cigarette Lighter Power” is DC AC stands for “alternating current” and means that the voltage and current “alternate” back and forth Grid-supplied electric power is AC, cycling 60 times every second, or at 60 Hz.

© 2005 Baylor University EGR 1301 Slide 17 This Concludes Lecture 20