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Electricity help needed please

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Two spherical conducting wires A and B are connected to the same potential difference. Wire A is three times as long as wire B, with a radius double that of wire B and resistivity doubles that of wire B. What is the power delivered to wire A to the power delivered to wire B?
The MCQ answers are:

  • Electricity help needed please -

    I assume your wires are round, not spherical. That is, they have a circular cross-section.

    If A has power P, and cross-section area a, length m and resistivity r, then its resistance

    R = rm/a

    P = E^2/R
    E^2/(rm/a) = aE^2/rm

    Conductor B has power
    (2a)E^2/(2r*3m) = 4/6 aE^2/rm = 2/3 P

  • Electricity - correction -

    double radius is 4 x area, so

    B has 4/3 the power.

    I assume the answer choice 4/2 is a typo, since usually fractions are reduced.

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