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  1. M

    Questions about Charging Speeds and Wattage

    sorry, I am not sure how to explain in correct physics terms I just want to understand how it is possible that a usb charger with an output capability of 2 amps can charge a device with an input capability of 1 amp significantly faster than a charger with an output capability of 1 amp? This is...
  2. M

    Questions about Charging Speeds and Wattage

    Ok, so that means that those websites are wrong then? It doesn't matter how high the output current is if the maximum current input stays the same? But how come people say their devices do charge faster if they use a charger with a higher output current? For example, I read people say their...
  3. M

    Questions about Charging Speeds and Wattage

    Hi, I'm not sure if this is a correct place to ask this, but i have a question about the charging speed for the usb chargers for phones and tablets. from what I have gathered, the device being charged is the one that pulls the current from the charger, so if a 1 amp input device is charged with...
  4. M

    Ohm's Law Homework

    uhh...it doesn't seem like you are even trying.. doesn't physics require you to have some knowledge of algebra at least...? you already have the equation right there: V = I x R all the problems give you 2 of the unknown variables.. why can't you solve for the one remaining variable?
  5. M

    Ohm's Law Homework

    no... voltage divided by the resistance = 9 / 18 = 1/2.... and yes, current is measured in amps
  6. M

    Ohm's Law Homework

    it is very simple.. the current equals the voltage divided by the resistance... and in first problem, the voltage equals 9 V (9V battery) and the resistance is 18 ohms.... so try to figure it out...
  7. M

    RLC AC Circuit f and ω

    i learned that ω is the angular frequency.. so am i supposed to use ω = 2 pi f for this problem? i am confused since my teacher keeps calling ω the frequency and not the angular frequency...
  8. M

    RLC AC Circuit f and ω

    Homework Statement I am given a RLC circuit with a AC power source (e.g. signal generator), and i want to find the reactance of the capacitor. Given: R = 2200 Ohms, L = .025 H, C = (1 x 10-9) F, V0 = 5 V f = 3000 Hz Homework Equations edit: Sorry i wrote wrong formula.. here is...
  9. M

    Charge of Capacitor in LC Circuit

    oops, i calculated wt and A wrong... now i get B = 1.99x10-6 and Q(t) = (1 x 10-6) cos(wt) + (1.99 x 10-6) sin(wt) Q(1) = 2.37 x 10-7 C Is this the correct answer for the problem?
  10. M

    Charge of Capacitor in LC Circuit

    sorry, I am only in a general physics with Calculus II class...so I am not sure how to help.. can someone confirm if my answer is correct?
  11. M

    Charge of Capacitor in LC Circuit

    i'm not sure what you mean by complementary solution... but for my problem, i solved for A = 1 x 10-6 C, and B = -6.37 x 1011 and then I did Q(t) = 1 x 10-6 cos(wt) + (-6.37 x 1011) sin(wt) = 2.23 x 1011 C is this answer correct? am i supposed to get an enormous charge at 1 second?
  12. M

    Charge of Capacitor in LC Circuit

    ok, I am still a little confused, since in the lecture, I did not learn these two equations: Q = Q0cos(ωt + θ) Q = Q0cos(ω[t - t0]), I was told that Q(t) = Acos(wt) + Bsin(wt), and that A and B depends on initial conditions Then, for initial conditions at t = 0, A = Q0, and B = 0...
  13. M

    Charge of Capacitor in LC Circuit

    ok, but i am not sure how to do this.. i thought Q0 was the initial condition charge, and it says at t = 0, the charge is 1.0 microC.. Isn't this the initial condition? I have no idea what to do with the other charge at the other time..
  14. M

    Charge of Capacitor in LC Circuit

    Homework Statement An LC circuit constructed of a 1 microF capacitor and a 1 microH inductor is set in oscillation so that the charge on the capacitor is 1.0 microC at t = 0 and 2.0 microC at t = 1.57 x 10^-6 s. What is the charge on the capacitor at t = 1.0 s? Homework Equations Q(t) =...
  15. M

    Current and Time in RL Circuit

    I used Io equal to E / R, voltage over resistance from Ohm's Law, because for "long, long time", the initial current is equal to that... so is my answer correct?
  16. M

    Current and Time in RL Circuit

    Homework Statement An emf of 10V is connected to the RL circuit (R = 10 Ohms, L = 1.0 H) shown below for long, long time (the switch is in position 1). Then, at t = 0 the switch is thrown into position 2. Find the current in the circuit at t = 0.2 s. When will the current drop to 0.001 A...
  17. M

    Charging a RC Circuit

    ok..., i used a graphing calculator now and i get 9.99 * 10^-9 C... is this correct?
  18. M

    Charging a RC Circuit

    ok.., i recalculated and now i get 1 x 10^-8 C... is this correct? is it exactly 1?
  19. M

    Charging a RC Circuit

    Homework Statement An RC circuit is made of a 2.2 kOhm resistor and a 0.001 microF capacitor. The circuit is connected to a 10V source of emf for 5 x 10^-5 s. What is the resulting charge on the capacitor after that? Homework Equations Q(t) = -ECe^(-t/RC) + EC , where E is the emf...
  20. M

    It is asking for the magnitude and direction of the electric field strength

    your constant C is equal to k = 1 / 4 pi e0, so the equations are the same..
  21. M

    Calculating the current supplied by a battery

    from the data you are given, it should be correct...
  22. M

    How many windings needed to generate Peak emf

    ok, thanks, the max sin = 1 helped a lot... so i found the answer to be N = 3183 turns is this correct?
  23. M

    How many windings needed to generate Peak emf

    Homework Statement A simple generator has a coil with dimensions 1.0 cm x 1.0 cm which is rotated at 60 Hz in 1.0 T magnetic field. How many windings (turns of wire) are needed to generate a peak emf of 120 Volts ? Homework Equations 1. emf E = - d (magnetic flux) / dt 2. magnetic flux = (B...
  24. M

    Calculate in rad or deg mode for sin(wt)

    Homework Statement A simple question: do i calculate in radians or degrees mode on the calculator for sin( w t) where w = omega(rad/s) and i am given w = 50 rad/s and t = 5 s Homework Equations The Attempt at a Solution Would i have to calculate sin(250) in radian mode since...
  25. M

    What does polarity of voltage mean?

    Homework Statement For part of my physics lab, I used an oscilloscope and approached a pickup coil with a bar magnet... and I saw that the line on the oscilloscope moved down when I removed the N pole of the magnet away from the coil, and the line moved up when I removed the S pole from the...
  26. M

    Magnetic Force, Moment, and Torque on Square Current Loop

    Homework Statement [PLAIN]http://img521.imageshack.us/img521/5139/physicsproblem.jpg [Broken] Homework Equations FM in uniform magnetic field = I L x B m = I A2 where A is the area, direction given by Right Hand Rule (perpendicular to plane of loop) T = m x B The Attempt at a Solution...
  27. M

    Magnetic field at point P

    Homework Statement #32, figure (e) http://www.physics.sfsu.edu/~nlepeshk/230/28_32.pdf" [Broken] Homework Equations Binfinite line = u0 I / 2 pi rperpendicular Bcircle = u0 I / 2R The Attempt at a Solution should I assume that the two horizontal lines are semi-infinite...
  28. M

    Line Current in Three Dimensions

    i am begging for help, the problem is due tomorrow, the only equation i was given for magnetic field due to line current was the one i used in the image, and i don't think i am expected to solve it by deriving the bio-savart law again..i need help please
  29. M

    Line Current in Three Dimensions

    i really need help with this problem , i am more confused than ever: is r perpendicular the distance from the point to the start of the current? in which case, it is sqrt(2)? or is it the perpendicular distance from the point to the z axis? in which case it is 1... how come i get a negative...
  30. M

    Line Current in Three Dimensions

    Homework Statement [PLAIN]http://img515.imageshack.us/img515/5139/physicsproblem.jpg [Broken] Homework Equations in the image The Attempt at a Solution I don't know if i placed the angles theta1 and theta2 correctly in the diagram..I feel like this is incorrect, since the value i...
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