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Negative voltage

  1. Mar 2, 2014 #1
    when a magnet is falling through a solenoid, voltage is produced.
    Once positive is produced and the when the magnet leaves the solenoid negative voltage is produced.

    Voltage is the energy lost by a unit charge when travelling from one point to the other.

    So if there is negative voltage produced, does this mean charge gains energy?
  2. jcsd
  3. Mar 2, 2014 #2


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    Voltage requires a defined path (though because the electric field is a conservative force, the actual path does not matter, only the endpoints). So yes, if you have a negative voltage, then a test charge would gain energy by following that path. Reverse the path and you have a positive voltage which is the energy you have to expend to move the test charge back to the starting position.

    EDIT: Should qualify that the sign of your test charge matters too. We are talking about a positive charge above. A negative charge would be the opposite.
    Last edited: Mar 2, 2014
  4. Mar 3, 2014 #3
    Whatever the sign of the voltage, and whatever the sign of the charge of the test charge, the field will make it move in a way that it gains kinetic energy from the field. It's dangerous to talk about potential energy, because the electric field is not conservative in the presence of a changing magnetic field.
    If you hook up a resistor to the solenoid, it will produce heat, both with a negative and a positive voltage across it.
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