Recent content by knowone

  1. K

    The speed of a metal wire on two rails with a magnetic field

    I solved these equations: εbattery-εinduced =IR, εinduced = vdB, and m(dv/dt)=IBd Then I= (εbattery-vdB)/R, thus m(dv/dt)=Bd((εbattery-vdB)/R). Using differential equation, v(t)=A(1-e-λt), where A = -εbattery/d2B2 and λ = d2B2/mR Here we added a arbitrary constant R. I'm reluctant to use it...
  2. K

    The speed of a metal wire on two rails with a magnetic field

    The power of the battery is εI and it equals Fv=IdBv. Thus εI=idBv and v= ε/dB
  3. K

    The speed of a metal wire on two rails with a magnetic field

    Homework Statement I tried to understand the problem b) and c).[/B] Homework Equations Faraday's law: ∇xE = - ∂B/∂t emf ε = Bdv Force : F =ma, Lorenz's force F=q(vxB) ==> ma = IdB Power : power of battery = εI, mechanical power of the wire = Fv The Attempt at a Solution I think I solved...
  4. K

    What are the main resources for learning physics on Physics Forums?

    I'm a SNU student in South Korea. I never had formal physics education before, and now I'm trying to catch up my school curriculum. I hope that I could give tips to other guys later.
  5. K

    The height of a dielectric material between two coaxial pipes

    Without L, how can I calculate the capacity? I differentiate the electrostatic energy of the conductor to obtain electric force inside the conductor. U= (V^2)C/2 and C changes with the total length of the conductor and the height of the oil. Of course the force do not contain L.
  6. K

    The height of a dielectric material between two coaxial pipes

    Homework Statement This is the exercise 10.6 from Feynman lectures on Physics 2. Two coaxial pipes of radii a and b(a<b) are lowered vertically into an oil bath. If a voltage V is applied between the pipes, show that the oil rises a height H. Show that H=(V^2)(κ-1)ε_0/[ln(b/a)ρ(b^2-a^2)g] where...
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