Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Potential energy

  1. Sep 19, 2011 #1
    1. The problem statement, all variables and given/known data

    This is not a real existing homework problem but I do have two questions.

    Q.1. In a circuit with a battery of 12 V, one always draws a scheme in which 0 V is written next to the negative terminal. Now, consider only a low resistance (and assume no short circuit will occur), is the potential at the negative terminal of the source near to 12 V (because of the low resistance) or is it always near to 0 V because the electrons lose/use their energy anyway, independing of the resistance they experience.

    Q.2. The temperature of electrons is often written in electron volts (eV). The temperature, does it depend both on the thermal velocity and the drift velocity? So a cold electron (at room temp) can have a lot of energy if it is accelerated (or does the thermal energy increases as well then) and a slowly drifting electron with a high temperature also has a high "electron temperature"?

    2. Relevant equations

    thermal velocity: sqrt(3kT/m)
    drift velocity: sqrt(2qV/m)

    with V the potential difference.

    3. The attempt at a solution

    Hours of search to a simple explanation but nothing found so far.
  2. jcsd
  3. Sep 20, 2011 #2


    User Avatar

    Staff: Mentor

    The potential at the negative terminal of the battery is always exactly 0 volts (for the cases you are considering). It is defined as being 0 volts, and doesn't change with the load. If the load draws a lot of current, the battery voltage will seem to drop, in which case the positive terminal is no longer delivering +12 volts, it may fall to +11 volts, or even less. Same thing happens when the battery is going flat.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook