22.10

A 6.60 uC particle moves through a region of space where an electric field of magnitude 1200 N/C points in the positive x direction and a magnetic field of magnitude 1.02T points in the positive z direction.

If the net force acting on the particle is 6.21x10^-3 N, in the positive x direction, find the components of the particle's velocity. Assume the particle's velocity is the x-y plane.

vx , vy , vz =

I just know we use the formulas:

F =qE
F=qvB

I can't figure how to get the velocities for the 3 components...

MP 21.62 part B (Assignment 4 #16) Practice Problem

The capacitor in an circuit ( = 140 , = 40 ) is initially uncharged.
PartB
Find the current in the circuit one time constant after the circuit is connected to a 9.0- battery.

I use this but didnt work

I = V/R (1-e^-t/RC)

When the problem said one time constant, does that always mean that t/RC = 1, or only the RC is equal to 1?

I think Prof gave the similar problem on the last quiz, where it asked the current after 2 time constant. And he just plugged the "2" into t/RC

Questions 1 to 6 from Friday's SI Session - Test 1 Prep

What were the answers for the 6 questions rom Friday's SI session for Test 1 Prep. I tried to solve the problems; however, I don't know if I did them correctly. So does anyone have the answers so I can compare? Thank you.

MP 21.48 part E (Assignment 3 #12) Practice Problem

Calculate the potential at point D.

I dont really understand what the figure is all about. And, it says that point A is grounded. What does that mean? Does it affect any other point? Can I know the potential at point B?

Thanks.

21.36 & 21.92

I'm having trouble figuring out 21.36 and 21.92 of the homework.

21.36
When two resistors, R_1 and R_2, are connected in series across a 6.0V battery, the potential difference across R_1 is 4.1 V. When R_1 and R_2 are connected in parallel to the same battery, the current through R_2 is 0.46 A.
Fine values of R_1 and R_2.



21.92
The equivalent resistance between points A and B of the resistors shown in the figure is 25 ohms. Find the value of Resistance R.

I'm having a hard time because there's no voltage given. Am I supposed to incorporate Kirchoff's rules somehow?

Checking the Blog

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Dante

Equipotetial problem on Wed, 3-17

Dante,
I am still questioning about the problem that Prof gave on wednesday, the topomap.
The question was how much work would it take to move +1.o micro coulomb of charge from A to B (where the potential of B is higher than that of A by 4V).
I remember you explaining it and the sign is negative?
Also read p.668 on the textbook, it says "positive charges accelerate in the direction of decreasing electric potential".
Does that mean that if it goes in the direction of increasing V, it decelerates? then the work is negative?
When work is needed, is the sign negative? or positive?

Signs always confuse me. I have problem with the sign of electric potential and potential energy as well.
Please help.

thanks

DC CIRCUITS LAB--setting up the circuit

What do we need to know in order not to blow the fuse? Anything else other than these?
And please correct me if I'm wrong.

1.) Red goes to red (positive) and black goes to black (negative)
2.) Ampmeter in series(part of circuit), voltmeter in paralel (just touch whats being measured)
3.) Red goes to white when measuring the current. When do we use the yellow?
4.) Turn the knob to 200mA. What number do we use when measuring V and R?


Thanks

Physics tests CAN save your life

4b hw 4

A clyndrical shell of uniform charge density P0 lies in a region a .<.r<.b. find the E-field in all regions and graph E vs. r.- its a cylinder with a smaller cylinder as its hole. (couldnt get the picture up)

FOR NEWCOMERS!

If you have not been to this blog before please read both the "Instructions" and "Welcome!" posts which are under the "February" folder in the "Blog Archive" on the right side. These two posts will tell you how I want you to post questions and answers!!

Thanks,

Dante

Remember the color patterns on the resistors in lab?

Assignment Due Date

Hey everyone! I think the prof accidentally set the due date for Mastering Physics homework for Saturday at 9am instead of pm.. just a heads up!!

21.66 - RC circuit

for this problem do we just plug in the values into the formula:

q(t) = C(emf) (1 - e^ (-t/T) ??

for some reason it isn't working out for me..

emf = 9V
R = 50.0 k Olms
C - 140 mF

it wants to find the time (t) it takes to charge the capacitor to 5.0V.

20.52

what is dielectric strength? how is it suppose to fit into problem 20.52? (first problem in hw 3)

4b problem from Tatoian's hw-3 #5 and #9

5.A Water drop of radius 2.0 micro-meters is suspended in the atmosphere where the E-field's value is 500 V/m . How many electrons are there?


9.A 120-keV electron is fired directly toward a flat large plastic sheet with a charge density of -2 micro C/m^2. From what distance must the electron be fired if it is just to fail to strike the sheet?

20.5

If accelerating plates are 1.05cm apart and have a potential difference of 2.05 x 10^4 V, find the change in electric potential energy for an electron that moves from one accelerating plate to the other.

don't know why i cant do this one, i've exhausted all my attempts except for one..

For all of the Bio Majors

Energy of a Capacitor

A parallel plate vacuum capacitor is connected to a battery and charged until the stored electric energy is U. The batter is removed and then a dielectric material with dielectric constant k is insterted into the capacitor, filling the space between the places. Finally, the capacitor is fully discharged through a resistor (which is connected across the capacitor terminals)

a. )Find "Ur " the energy dissipated in the resistor Express your answer in terms of "U" and other given quantities.

b.) Consider the same situation as in the previous part, except that the charging battery remains connected while the dielectric is inserted. The battery is then disconnected and the capacitor is discharged. For this situation, what is "Ur" , the energy dissipated in the resistor. Express the answer in therms of U and other given quantities.

im a little confused, the resistor is throwing me off. How do i approach this problem?? How do i answer these in terms of "U"?

Homework Conceptual Question 20.4

The question says:

A proton is released from rest in a region of space with a nonzero electric field. As the proton moves, does the electric potential energy of the system increase, decrease, or stay the same? Explain

Through trial and error I know that it decreases ;)

I just dont know why??

help?

"Nerd Sniping" - XKCD.com