DOC PREVIEW
CU-Boulder PHYS 1120 - Lecture Notes

This preview shows page 1-2 out of 7 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 7 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 7 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 7 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

11Preclass est9How much money will a typical person (not you :-)from this class earn in their entire lifetime? (in 2007 dollars)?(Don’t just guess, try to estimate the answer)A) $2-4 MillionB) $20-40 MillionC) $200-400 MillionD) $2-4 BillionE) How could I possibly know this?2Preclass est9How much money will a typical person (not you :-)from this class earn in their entire lifetime? (in 2007 dollars)?(Don’t just guess, and don't be fanciful - try to estimate the answer)A) $2-4 MillionB) $20-40 MillionC) $200-400 MillionD) $2-4 BillionE) How could I possibly know this?$30k/year? $100k/year? …. Let's call it $70 k/yrWork from age 25 to 65? That's 40 years…$70k/year * 40 years = $3E63Cool holiday LEDs sell like hotcakesRegular lights use 40 to 150 kilowatts an hourBy Ryan Morgan (Contact)Thursday, November 29, 2007…To drive that point home, Powell said, the city employees hosting the giveaway pluggedthe traded-in traditional lights into a kilowatt meter. Most strands used 40 kilowatts anhour, while others used as much as 150 kilowatts. LED lights — which are often brighterthan regular bulbs — use just two kilowatts hourly, she said."When people saw that, their jaws just dropped," she said.24CAPA #13 tonightNew online participation survey is still up! (But not for much longer)Reading: 34.6 (don't stress about the math, focus on the concepts!)New pretest available for next Tuesday._________________________Last: Inductors, and AC circuitsToday: AC circuits, Maxwell's equationsNext: More of Maxwell!! Vrms= Vpeak/ 2Pave= Ppeak/2(P = I V, as usual)6Light bulbs and appliances with motors (vacuum cleaners,blenders, …) use AC Voltage to operate.But devices with electronic circuits (TV’s, computers, phones,…) need DC Voltage (constant) to function.The “power supply” in TV’s, computers, etc. convert ACVoltage from the wall into DC Voltage (typically 2-15 Volts)that the circuitry needs.7CT 33.36A 600 Watt hairdryer is attached to 120 VACcircuit. What is the peak current through thehairdryer (to within 5%)?A: 0 A B) 5 A C) 7 A D) 10 AE) OtherP = IV, which means P(ave) = I(rms)* V(rms)600 W = I(rms) * 120 V => I(rms) = 600/120 = 5 A.But I(peak) = I(rms)*Sqrt[2] = 5*1.4, about 7.! rms = peak / 2(P = I V)38CT 33.37The instantaneous power consumed by my De-luxe ToasterOven looks like this as a function of time:9CT 33.38Which of the following is correct? P ave V rms I rmsA: 1200 W 120 V 10 A (=1200/120)B: 1200 W 170 V 7 A (=1200/170)C: 600 W 120 V 5 A (= 600/120)D: 600 W 170 V 3.5 A (=600/170)E: None of the above is right.1200 W10CT 33.39What is "T" in the picture (in the USA)?A: 1/30 s B: 1/60 s C: 1/120 s D: Other411AC Voltage is used to distribute power to homes (rather thanDC Voltage).12Electrical power is transmitted from power plants to citieswith big aluminum power cables.Much energy is wasted because of resistance in the cables,the cables heat up (i2R losses). To reduce this waste, poweris transmitted at very high voltage (100 kV to 1 MV !)constantcity) plant to from( == iVPSet by the needs of the city and the capacity of the plant.13DC versus ACLots of good books on the scienceand the people involved.51415Magnetic Energy DensityRecall that for a capacitor C, there is stored potentialenergy in the electric field.221CVU =The energy is stored in the electric field and the densityis:20||21EVolumeUuEv!==16For an inductor L, with current i, there is stored energy inthe magnetic field.221LiU =The energy density in the magnetic field is:20||121BVolumeUuBvµ==617UU212 1 I I The same current i flows through solenoid 1 and solenoid 2.Solenoid 2 is twice as long and has twice as many turns assolenoid 1, and has twice the diameter.(Hint) for a solenoid B = µo n i )What is the ratio of the magnetic energy contained insolenoid 2 to that in solenoid 1, that is, what isA)1 B) 2C) 4 D) 8E) None of these.B is the same in both solenoids (same n = turns/length!) soboth solenoids contain the same energy per volumeu = U/vol = B2/(2µo).The larger solenoid has 8 times the volume (2X the length, 4Xthe cross-sectional area) so it has 8 the energy.Clicker Question19Faraday's Law:! "= #d$magdt20EMF around a (stationary) closed loop is defined as: ! "=v E # dv l Loop$!!"#="surfLoopAdBdtdldEvvvvAnd thus Faraday’s Law can be written as:721A changing B-field creates a new kind of E-field.BIf B is decreasing  E-field is CCWEBEIf B is increasing  E-field is


View Full Document

CU-Boulder PHYS 1120 - Lecture Notes

Documents in this Course
Circuits

Circuits

18 pages

Circuits

Circuits

10 pages

Review

Review

8 pages

Vectors

Vectors

6 pages

Vectors

Vectors

6 pages

Magnetism

Magnetism

17 pages

Questions

Questions

13 pages

Magnetism

Magnetism

22 pages

Questions

Questions

24 pages

Answers

Answers

12 pages

Optics

Optics

24 pages

Circuits

Circuits

11 pages

Questions

Questions

20 pages

Voltage

Voltage

9 pages

Questions

Questions

19 pages

Review

Review

57 pages

Inductors

Inductors

22 pages

Questions

Questions

10 pages

Questions

Questions

10 pages

Questions

Questions

12 pages

Load more
Download Lecture Notes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lecture Notes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lecture Notes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?