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Potential Difference and Current

  1. Feb 16, 2014 #1
    1. The problem statement, all variables and given/known data

    Wires 1 and 2 are identical except that they are each made of a different material. The one end of wire 1 is connected to one end of wire 2. The two remaining ends are connected across a battery and current flows through the two wires. Is the potential difference is wires 1 and 2 the same or different? Is the current in wires 1 or 2 the same or different?

    2. Relevant equations

    R=(ρL)/A
    V=IR

    3. The attempt at a solution
    The resistivity would change because the material changes; therefore, the resistance changes. If the resistance changes, the current changes. Potential difference remains the same. Is this correct?
     
  2. jcsd
  3. Feb 16, 2014 #2
    Think about this, if you have two wires connected in series but they don't have the same current flowing through them, what happens at the point where they meet? If the current is higher in the first wire? In the second?
     
  4. Feb 16, 2014 #3
    If the current is higher in the first wire, then the first wire must have a lower resistance. If the current is lower in the first wire, then the first wire must have a higher resistance.
     
  5. Feb 16, 2014 #4

    gneill

    User Avatar

    Staff: Mentor

    If current were to be different in the two segments, wouldn't you end up with some continuous positive or negative charge building up where they connect? How could a continuous buildup of charge be sustained without catastrophic consequences?

    The rule is, series connected components (including wires) carry the same current; What goes in one end of a wire must come out at the other end at the same rate.

    If the wires have different resistivities, and hence difference resistances, you should be able to consult Ohm's law to see how the potential differences across the individual wire segments will behave, given that both segments MUST carry the same current.
     
  6. Feb 17, 2014 #5
    If it were true the current would change, I wouldn't have to pay for electricity, sadly it doesn't work like that :( Something does change, but it is not the current. In a series connection, say you have some consumers A B C with resistances, how would you calculate the total voltage in the series?
     
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