Honors Midyear Review

Midyear reviews will continue until Wednesday of next week: Monday and Wednesday Am and Tu and Thu PM.

AP Tests

The last wave test shows you had your mind on the break, not on physics. Do not take your eye off the ball again until after the exam. We are behind last year and I will turn up the heat.

Midyear exam review will continue through next Wednesday of next week. Tuesday mornings and Wednesday and Friday PM

AP Labs

Lab performance has gotten pretty shaky. Too many are coming in late. Some are very slipshod.

The standing wave labs were mostly fair or worse. You werw supposed to compare the c from sqrt( FT/mu) with the c from 2x Lloop (i.e. lambda) x the known frequency, 60 Hz. Alternatively you could compare the frequency from the slope of the graph of sqrt(FT/mu)vs lambda with 60 Hz and see if that gave you reason to believe c = sqrt(Ft/mu).

Most of you found f from the slope ( as above) and then multiplied that f by lambda to get c and then compared thus c to the one from sqrt(FT/mu). In other words you compared c to (c/lambda) x lambda. Guess what, they come out virtually equal. What amazes is me is how many of you do not realize what you are doing when you do this.

Some of you canceled the sqrt sign in equations like A/B =sqrt C/sqrtD to come up with
A/B =C/D. You cannot do that, or at least you cannot do that and still have a bona fide equation.

Conclusion that say we proved something better list the equations that were confirmed not just say all the ones we used.

Honors Fluids Review

Problem E.4

The surface of the water at the top of the tower is at 101,000 Pa. The end of the pipe is also open to the air so it is at 101,000 Pa. Thus P1-P2 = 0. Sorry if my reference to the pond confused you. I was just trying to help you picture a physical situation. As usual, we approximate the velocity in the tower as negligible compared to the velocity right at the pipe outlet. I am sure you can take it from there.

Enjoy the rest of your break.

Dr. Cherdack

Honors Project Assignment

See the assignment from December 20 and do it for real with feeling this time. Make sure you have at least one project meeting. Also stay tuned here to see if there is any more info on your part of the plant.

Honors Archimedes lab densities

Aluminum 2700 kg/m^3
Brass 8400
Copper 8900
Iron or Steel 7900
Lead 11300
Zinc 7100

Honors Extra Help problem

Given Reaction: D +He 3 goes to p(roton) + He 4 + additional 3.0x10^-12 J.
Initial vD = 6x10^6; total momentum =0

Find the initial v of the He 3. Find total KE before collision; find closest distance, r using initial KE = PE at closest approach; find KE of proton after the reaction ; find vp and vHe 4.

Calculators

Several calculators including students' as well as my spares have disappeared from room 506 in the last two months including one yesterday. This is the first time in seven years that I have had this problem. Please check and make sure you have your own. I do have one that is new to the room and it may be yours,but in any case if you have someone elses be good enough to return it.

AP Unit 10 schedule

The test is on 3/4 and ignore the days after 3/4 on your schedule. I did not delete those extra rows (probably because they jumped to the next page while I was editing and I didn't notice them.)

Science Awards

Not that any of you would deserve any of these but here is some info:

The 2010 RHS Science Award Applications are now available! If you are a junior or senior who excels in math and science, consider applying for one or more of these awards. Information and applications can be downloaded from Naviance or picked up from Mrs. Shadis in guidance. Applications are due March 5th.

AP Again - Time is running out

Dear AP Teachers,

Please remind your students that these are the last few days to register for Advanced Placement exams! The Community Pass system will shut off at 11:30pm on Friday, February 19, and no late registrations will be accepted. The same information and instructions regarding registration that were sent home can be found on the Guidance Department Web site under the "Advanced Placement" tab. Any questions can be directed to me or Linda. Thanks!

Jill

AP Exam Registration

According to a list I just received, 14 of you have not signed up for the AP Physics B test yet.
Is this the thanks I get for slaving endless hours over a hot computer to prepare you for this ultimate experience in academic revelry? What are you waiting for, June?

Sign up now.

Think of those poor deserving minions with their noses to the grindstones at the College Board. Where will they be without your $85 ? On the street that's where; and they'll have you to blame for it. ( well maybe there noses will stop hurting)

AP Waves item and The Schedule for ElectrostaticsS

1) The other thing I noticed on the tests was that many of you confuse particle velocity v and wave speed or wave velocity, c. This is one reason I always use c for wave speed or wave velocity and v for material particles. v particle max does = omega A but this has virtually nothing to do with c which is independent of frequency and amplitude. Particles oscillate about their equilibrium points with displacements and v's that vary harmonically. Waves travel from one end of a medium to the other ( and yes they may reflect and travel back but not with an oscillation rate of omega). The wave speed (or wave velocity) does not vary as the wave travels and is independent of A and omega.

2) Here are the new schedule and materials:

http://h1.ripway.com/DrCherdack/APUnit10ElectStSched10.doc

http://h1.ripway.com/DrCherdack/NotesElectrostatic3-08r1.doc



http://h1.ripway.com/DrCherdack/UnitAP10ESproblemsheet.doc

http://h1.ripway.com/DrCherdack/Unit10Worksheet1.doc

http://h1.ripway.com/DrCherdack/Unit10Worksheet2.doc

http://h1.ripway.com/DrCherdack/Unit%2010%20Worksheet%203.doc

http://h1.ripway.com/DrCherdack/Unit%2010%20extra%20problems.doc

Honors

Test results were very disappointing. It seems that anything not presented within the last 48 hours is gone.

Many of you have forgotten all we did about circular motion and the meaning of angular speed and how to find angular acceleration. Much of the work we did on orbits in magnetic fields is also gone.

Many of you tried to apply the equation for force on a wire carrying current to a single charge. What was the length you would use.

Despite words on the test and a message on the board and the nature of the picture on the test many of you assumed that the d which was clearly shown as the distance from a wire to the point where you were asked to find the field was the diameter of something and therefore the radius to be plugged into the formula had to be 1/2 of d. This was done after frequent reminders that r was the distance from the point of measurement of the field to the wire creating the field and was called r because the field lines make circles of radius r around the wire.

Almost all of you forgot that the force on a charge in a magnetic field is perpendicular to the velocity and the field. The majority of you do not even know how to find the area of a circle.

Many of you tried to find the field from a single wire by using an equation we developed for solenoids. Where did you get the number of turns from?

Lay a solenoid on its side and h becomes length, right. Most of you got that right and then decided that 15 cm is 15 m. Did you really think the solenoid was 50 feet long?

Not one of you you could turn the flow of charge into a current density. Electrons flowing to the left are a current to the right. The number of moving electrons per cubic meter times the area times the average velocity TIMES THE CHARGE PER ELECTRON gives the current doesn't it? If the area is 1 square meter then then the current density, J, is I/1

You folks will have to decide if we are honors classes this year. Plugging numbers into formulas whose meaning and whose basis for correctness you do not comprehend is not honors work.

AP Test results

1) AP results weren't bad, but it was a very straightforward test. Many of you still don't have the basics of algebra or physical relationships down. Frequency is waves per second. If six waves pass in thirty seconds then f =6/30 NOT vice versa!!!

Many of you could not find omega given f. Shame on you : 2 pi radians per cycle therefore 2 pi radians per sec per cycle per sec ....... or omega = 2 pi f.

Those are the biggies I can recall right now. We've got a lot to do in the next 3 days so the quiz will be Thursday.

AP Doppler Shift

Better late than etc. etc.

http://h1.ripway.com/DrCherdack/DopplerEffectTotal.doc

Honors Unit 10 Fluids

Here is your schedule etc. for our exploration of fluids. We will try to prevent HSPAs from interfering with our learning.

http://h1.ripway.com/DrCherdack/HonUnit9Fluids10.doc

http://h1.ripway.com/DrCherdack/NotesonFluidDynamics.doc

http://h1.ripway.com/DrCherdack/Review%20Sh%20Fluid%20DynamicsA.doc

More on Waves: 4 Items

1) As noted earlier several of you have decided that wavespeed increases if frequency does. Once again, this is not true and the equation lambda f = v is very misleading and should be written as lambda = cT or lambda = c/f. This properly indicates that the two independent quantities c and f both affect lambda. Wavespeed is given by sqrt(FT/(M/L)) for transverse waves and sqrt(Y/density) for longitudinal waves. See notes on these.

2)There is a velocity affected by the frequency but pay close attention to the following: By now you should have noticed that I never use v for the wavespeed, I use c. The wavespeed is not the velocity of a physical particle. No matter is moving at speed c. Matter moves at a velocity which is determined by the frequency and the amplitude because the matter is oscillating. For example, in a horizontally traveling transverse wave, where y = A sin ( omega t - kx), the matter is going up and down, with a velocity = omega A cos (omega t -kx). This physical velocity IS NOT the wavespeed. Omega here is 2pi f as usual and is also 2pi c/lambda. Once again, the frequency, f, and therefore the omega depend on the oscillation causing the wave. For example the frequency with which you moved your hand from side to side in the lab. Note that wavespeed is constant for the wave traveling in a medium, while the particle, or matter, velocity varies harmonically , as you would expect in a harmonic oscillation.

3) Nearly all of you got the first part of the very last question wrong ( item 8 at the end of the lab). See my notes so see the correct way to add them and BE MORE CAREFUL. Not everything is the easiest possible.

4) In order to answer a question, you must read it it. If they ask about phase answer about phase, not amplitude, not energy, not your favorite flavor. PHASE!!!! Waves can be represented as say y = A sin (omega t -kx) omega t -kx is th angle, the argument of sin , the PHASE, i.e what part of a cycle the wave is in.

Waves again

I warned you several times and still many of you act as if f lambda = c means that increasing f increases c. This is not true, increasing f merely reduces lambda. This is why I urge you to think of the relationship as lambda = cT = c/f.

Another way to misuse this equation is to suppose that if the wave speed changes as you enter a new medium the frequency must as well. It is the wavelength that changes as the speed changes. The number of pulses per second doesn't change when you cross over. Every you pulse you send from one medium reaches the other and the number of pulses you send per second equals the number of pulses per second that reach the other end of the first medium and the beginning of the new medium. [Unless it is moving towards or away from you, a complication we will deal with next week.]

AP Labs

1) Waves: There are few ideas that are getting confused here. In the traveling wave (slinky) lab you created the wave at whatever frequency you chose to shake the end of the slinky. This frequency was imposed by you and had nothing to do with the properties of the spring. The wave speed, c, was determined by the mass per unit length and the tension and that's all[ except for friction with the floor which tends to slow things a bit, especially for waves that are weak in movement any way]. So frequency and wavespeed are independent.

Do not confuse this externally imposed frequency with the resonant frequency of an oscillator given by 2 pi omega. The frequency in the wave lab was imposed by you, not by the materials.

For the questions referring to two differing media ( like that Latin , huh?) note that except for the floor friction, which was substantial for the coil ( heavy spring), the tension in the two media had to be equal. You can't pull harder on one end then the other unless the springs were accelerating down the hallway. If they were, I missed it.

2) Standing waves. A standing wave is a different situation. This is where a single pulse, or small imposed oscillation of a frequency which is related to the wavespeed, causes large oscillations because waves reflected from both ends reinforce each other. In this case, say for two fixed ends L meters apart, the harmonic frequency IS related to wavespeed by f = c/2L or 2 c/2L or 3 c/2L etc. [This is because the wave must satisfy the condition that wavelength = 2 L/integer so that both ends are nodes and nodes are an integer number of half wavelengths apart. This is the same as requiring that reflections from the two ends cause the right kind of interference at nodes ( destructive) and antinodes (constructive).] Since in this case f = integer c/2L, a higher wavespeed and higher frequency are associated. If you try to impose a frequency other than a harmonic you will not get a standing wave pattern.

Wednesday's Attendance

While I would like to express my appreciation to those who came to class in the stands today, I can't help but be somewhat disappointed by the 20% absentee rate. I thought you folks were made of sterner stuff.

Wednesday

Ugly rumors of a snow day tomorrow are being spread. Since I know that none of you can survive a day without physics class, we will meet at regular class hours tomorrow. If necessary, we will meet in the stands on the south side of the turf (yes I know that's the visitor side, but it will be warmer on the south side, after all it's closer to the equator, isn't it?) Dress warmly and bring your waterproof notebooks and put plenty of antifreeze in your pens.

Also bring some snacks for the sled dogs, they can get pretty nasty when they are hungry.

PS If am not there DON'T wait for me.

Group Reports

Both AP and Honors should have their first study group meeting reports for this quarter in by Friday. Date (not "Sunday"and time; subject (not just "homework" or "problem sheet" tell me what topics you covered); attendees; and place are required. One per person.

Fire Drills

FYI:

we will be having the following two fire drills on Wednesday, February 17th:

1. End of period 5 @ 11:20 a.m.
2. End of period 8 @ 1:35 p.m.

Note the times and don't expect to remember to remind you.

LABS

See post of December 1 re late labs.

AP problem 2 Unit 9 WS 2

Apologies, linear mass density is .0085kg/m not /m^3 and answer is in N not Hz.

Honors problem

A plasma has a current density of 8x10^5 amperes/m^2 in a field of 4T. However the field is not perpendicular to the current, it makes a 9.5 degree angle( 1/6 radian) to the current. What is the force on a cubic meter of plasma from the magnetic field?

Honors and AP

The media center printers are being overloaded. Please refrain from printing large downloads on teh media center printers.

Extra Help Schedule

AP: Tues AM, Wed Fri PM

Hon: Tue Thu PM

Initial emphasis is repairing midyear exam damage

Other times as available

Honors Shedule Unit 8 Magnetics

Here it is [note on worksheet that 105 is 10^5]. Its not as bad as it looks because you have read much of this stuff once or twice already.

http://h1.ripway.com/DrCherdack/HnrUnit8Magneticsch10.doc

http://h1.ripway.com/DrCherdack/Notes%20on%20magneticsR8.doc

http://h1.ripway.com/DrCherdack/TokamakFields.doc

http://h1.ripway.com/DrCherdack/Magnetics%20Worksheet%20M.doc

http://h1.ripway.com/DrCherdack/MagneticsWorksheetM2.doc

http://h1.ripway.com/DrCherdack/Rotational%20Motion%20in%20Magn.doc

http://h1.ripway.com/DrCherdack/NotesMagFldsandTransprtPrt1%20.doc

AP Urgent Exam Registration

If you plant to take the exam read this Message from guidance:

This is just a reminder that AP Registration begins today, and runs through 11:30pm on Friday, February 19. Your students all received a letter at home with details and instructions for using Community Pass; that letter and all other links and information can be found on the Guidance web site, on the AP page (http://www2.bernardsboe.com/Guidance/Advanced_Placement_Testing.aspx).