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Homework Help: Electormagnitics Quests relating coaxil cables and other

  1. Aug 22, 2008 #1
    Hey Guys i have tried to attempt some of these questions i just dont understand where to start from i need the main formulas that can help me do these questions thanks alot

    a) coaxial line consists of an inner conductor of radius RA = 1 cm
    and outer conductor with an internal radius of RB = 10cm. The
    internal conductor is charged positively with a linear charge density
    of ρℓ = +100 nC/m. Calculate the potential difference between RA
    and RB.

    (ii) Find the total effective capacitance of the coaxial line described in
    (i) if the length of the line is 30 cm and the region between the
    conductors is filled with dielectric with relative permittivity of 2.5.

    (e) A coaxial line consisting of inner and outer conductors with unknown
    radii is located in zero gravity conditions and has a potential difference of
    8 kV between electrodes. A particle with a charge of +1 mC and with a
    mass of 40 g is located almost on the surface of the central, positively
    charged electrode.

    The particle is released from its location with zero velocity initially and
    starts to move towards the opposite electrode. Calculate the velocity
    which the particle will have when it reaches the opposite electrode.
    Last edited: Aug 22, 2008
  2. jcsd
  3. Aug 22, 2008 #2
    Plz guys i need an urgunt help with these quest :(
  4. Aug 22, 2008 #3


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    Homework Helper

    1)The question appears to be stated improperly. The inner conductor is not of negligible radius yet the linear charge density, instead of the surface charge density is given. But I'm fine if it implies that ρ is the charge density of a ring of negligible thickness around the conductor.

    Use Gauss law here to find E. Then use a formula to obtain the potential difference between the conductors. Once you've done that, use a general capacitance formula to determine the capacitance.

    2)You're given the potential difference. Use that to determine the work done in moving the charge from one electrode to another. You should be able to determine the final velocity by using a formula and the work-energy theorem.
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