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  1. 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...
  2. 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...
  3. 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) =...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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...
  10. 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...
  11. 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...
  12. M

    Right Hand Rule for Magnetic Fields

    Hi, I am wondering if anyone here has heard of or can explain this variation of the right hand rule: Most websites i see tells you to point thumb in direction of current and curl the fingers, and the direction of the magnetic field is the direction you're curling. But my professor uses a weird...
  13. M

    Find Magnetic Field of Infinitely Long Line Current

    Homework Statement Homework Equations B = u0 I / 2 pi r (perpendicular) The Attempt at a Solution This seems like a simple plug in values equation, but the 3-dimensions is confusing me, and I can't figure out what the value of r(perpendicular) should be, and what the direction...
  14. M

    Find Current with Kirchhoff's Rules

    Homework Statement I just need to check if my answers are correct [PLAIN]http://img99.imageshack.us/img99/5139/physicsproblem.jpg [Broken] a) Find # of junction points b) Find # of arms c) Find currents in all arms by applying Kirchhoff's Rules Homework Equations Current in = Current out...
  15. M

    Principle of Energy Conservation for Two Protons?

    Homework Statement Two protons (radius 10^-15 m) are headed directly toward each other with equal speeds. Use the principle of energy conservation to compute the minimum kinetic energy and initial speed each proton must have if they are to collide. Homework Equations W = delta K W =...
  16. M

    Moment of Inertia using density of Earth

    Homework Statement The density of the Earth, at any distance r from its center, is approximately p = [14.2 - 11.6 r/R] x 10^3 kg/m^3 where R is the radius of the Earth. Show that this density leads to a moment of inertia I = 0.330MR^2 about an axis through the center, where M is the...
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