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DC Stuff Continues. W7D3. This Week + peek into the future. Quiz on DC Circuits Complete Unit #8 Be sure to download the next unit from the website. Best Guess about Exam #2 Monday, October 18 th Yes, that’s in about one week! Review session on Monday morning @ 7:30AM

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DC Stuff Continues

W7D3


This Week + peek into the future

  • Quiz on DC Circuits

  • Complete Unit #8

    • Be sure to download the next unit from the website.

  • Best Guess about Exam #2

    • Monday, October 18th

    • Yes, that’s in about one week!

  • Review session on Monday morning @ 7:30AM

  • Next major topic will be MAGNETISM.


Reading Summary /next exam

  • Chapter 18

    • Parallel Plate Capacitor (548)

  • Chapter 19

    • Sections 19.1-19.4

    • Section 19.5 – Only what we cover in class

  • Chapter 20

    • Section 20.1-20.4

    • Section 20.6-20.11

    • Section 20.12 – A covered in clss


last time we discussed a real battery


E= enf=internal voltage

Internal resistance reduces

the effective voltage of the

battery.

E

Use this in the experiment with the W wire!


the Kirchoff corporation.

  • From the current unit:

    • The current entering a node is equal to the current leaving it.

      What goes in must come out!

I

Direction doesn’t matter.


The Loop Equation

If you start at a point in a circuit and go around the loop and return to the same place, the change in potential is zero. Or: The sum of the voltage rises = the sum of the voltage drops=0

I


The real deal-Sometimes you can reduce a circuit


Overview dc circuit preliminariesw7d1

October 4, 2010


This week

  • We continue our exploration or DC circuits.

  • There is a WebAssign which you should be able to answer later in the week. Feel free to actually read the textbook and start sooner!

  • There will be a QUIZ on Friday.

  • Examinations have been returned.


Be aware

  • The “exploration” approach leaves much out of the classroom discussion.

  • Some of this required material may be found in the textbook.

  • WebAssign can serve as a guide to some of this.


Current

I

L

-

+

A

V


ANOTHER DEFINITION

(Average) Current Density


The total charge moving from A to B must be the

Same or charge would build up at the interface.

I

A B


NOTE

  • Electric Current is DEFINED as the flow of POSITIVE CHARGE.

  • It is really the electrons that move, so the current is actually in the opposite direction to the actual flow of charge. (Thank Franklin!)


Charge is moving so there must be an E in the metal conductor!


Ohm

  • A particular object will resist the flow of current.

  • It is found that for any conducting object, the current is proportional to the applied voltage.

  • STATEMENT: DV=IR

  • R is called the resistance of the object.

  • An object that allows a current flow of one ampere when one volt is applied to it has a resistance of one OHM.


Ohm’s Law


Resistivity and Resistance

I

L

-

+

A

V


How?

A wire has a resistance of 20 Ω. It is melted down, and from the same volume of metal a new wire is made that is three times longer than the original wire. What is the resistance of the new wire?


The Real Deal


A current I flows through a device. The difference in potential

from one side of the device to the other is V. How much POWER

is dissipated in the device?


Reading materials

  • Sections: 20.1-20.4

  • Sections: 20.6-20.9

  • Watch for a new WebAssign that will be due on TUESDAY evening so we can get back on schedule.


DC CircuitsW7D2

Instructor BindellCourse 2054 Fall 2010


Calendar

  • Today

    • Some DC Issues not yet covered

    • The usual review stuff

    • Continue on Units 7 & 8

    • There is a new WebAssign on DC. Watch for more, so don’t wait to get started.

  • Friday

    • The usual quiz

  • Next week – We should complete the chapter with an exam to be scheduled shortly thereafter.

    • Start studying NOW.


DC Circuits III

W8D1


This Week

  • Finish the chapter including the next unit.

  • Friday – Quiz

  • Next Monday or Wednesday – EXAMINATION #2

Noooo!! –

Not another one!!

Problem Review as usual at 7:30 AM

Monday – Rm 218 CLA I


Reading Summary /next exam

  • Chapter 18

    • Parallel Plate Capacitor (548)

  • Chapter 19

    • Sections 19.1-19.4

    • Section 19.5 – Only what we cover in class

  • Chapter 20

    • Section 20.1-20.4

    • Section 20.6-20.11

    • Section 20.12 – A covered in clss


About that experiment

  • The meter doesn’t seem to function correctly for this experiment

  • Significant contact resistance … the pressure on the contact is important. The meter works better at higher currents.

  • Here is data from another meter.

  • Use this data and bypass the experiment.

  • Sorry about that!


From Unit 08

A

B

Battery with

internal R

C

W Wire

D

V=1.494,


Current Measurement – Keithley MeterLeast Square Estimate

Current

ma

Length – 30 cm units


PREVIOUS SLIDES ARE POSTED ON THE WEBSITE


Find the magnitude and direction of the current in the 2.0-Ω resistor in the drawing. (Let R = 3.0 Ω and V = 2.5 V.)

=2.5

=3 ohm


A portable CD player operates with a voltage of 4.5 V, and its power usage is 0.21 W. What is the current in the player?


Back to WORK!


An especially violent lightning bolt has an average current of 1.15 103 A lasting 0.146 s. How much charge is delivered to the ground by the lightning bolt?


Two wires are identical, except that one is aluminum and one is iron. The aluminum wire has a resistance of 0.20 Ω. What is the resistance of the iron wire?

0.688Ω


The filament in an incandescent light bulb is made from tungsten. The light bulb is plugged into a 60 V outlet and draws a current of 0.96 A. If the radius of the tungsten wire is 0.0050 mm, how long must the wire be? 0.0877m


Adding R’s

L

L1 L2

Series Resistors ADD


Parallel Resistors

R


Bulb D is removed, what happens to the brightness of bulb B?

ABrighter

BDimmer

CNo Change

DIt goes out

EHuh??


Play it again Sam …


TURN IN UNIT 5 NOW

Back To Work!!


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