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A question about electric energy

  1. Aug 26, 2014 #1
    Hi guys
    I know that in a 6 volt battery 1 columb of charges gain 6 joules of energy do they gain potential or kinetic energy as they move from the negative terminal to the positive terminal ????????
    And how different the energy in Ac electro motive force
     
  2. jcsd
  3. Aug 26, 2014 #2
    Regarding your energy conversion question, it is entirely dependent on the circuit. Say for example you have your battery and have no wires to complete the circuit. A circuit that isn't closed is referred to as an open circuit. A circuit that has infinite resistance. In this case, your potential energy remains as potential energy.

    Now say for example you have a closed circuit that creates an electric current. Depending on your circuit, most of your energy is converted from the batteries stored energy (potential energy) to heat (thermal energy). However, the rate at which this energy is converted is dependent on the circuit.

    Let says you have a closed circuit that has ZERO resistance. This is known as a short circuit. In a short circuit, you theoretically have infinite power consumption, and remember, power is simply the rate at which energy is consumed or produced. So for an application that has infinite power consumption (or an infinite rate of energy consumption), you have the batteries potential energy instantly being converted to thermal energy. Things get really hot! If you ever short circuit a small battery with a piece of tin foil, you will notice that the piece of tin foil gets very warm. This is a perfect example of electric potential energy is converted to thermal energy.

    Someone correct me if I'm wrong, but you could also say that the potential energy is being converted to kinetic energy due to the mass and velocity of electrons. But when dealing with circuits, the main concern is typically the thermal energy produced.

    Regarding your second question of AC power, could you be more specific what you are asking?
     
  4. Aug 26, 2014 #3
    Nope I meant that when negative charges are attracted to the positive terminal do they spend or gain energy
     
  5. Aug 26, 2014 #4
    Okay let's try this again sticking with the short circuit example.

    In a short circuit, you theoretically have zero resistance. Because there is very little resistance you get a high current. Current is simply the flow of charge past a given point within a certain time increment. The SI unit of current is the Ampere which is defined as 1 Coloumb of charge per 1 second flowing pass a given point.

    The charges don't spend or gain energy, they simply convert energy. When the charge is located in the battery, the energy is potential energy. When you have a current within a circuit, that potential energy is converted into kinetic energy because you now have moving charges.

    Going back to the short circuit, you have a circuit that draws a very high current. Because the current is high, you get a lot of collisions between the moving charges and the conductor. This generates heat.

    Under ideal conditions where there are no power losses due to heat, the answer to your question would be that the charges do not spend or gain energy, they simply have their potential energy converted to kinetic energy. Realistically however, the moving charges will produce heat and some energy of the charge has now been lost.
     
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