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Fundamental Questions.

  1. Nov 15, 2005 #1
    I am confused with some fundamental things...

    Does voltage and current go in opposite direction when represented in a drawn circuit?

    Does current go the way opposite to the actual direction of electrons flow?

    In an AC signal, for example, a generator is placed at point B and it's connected to point A to the left and point C to the right, does the voltage actually go to point A first and then point C and continue the pattern?

    And does short circuit mean a malfunctioning circuit and open circuit means a circuit that's working or allowing eletron flow.

  2. jcsd
  3. Nov 15, 2005 #2


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    That depends, there are really two conventions used to tell how the current flows - conventional method and the electron flow method. The conventional method has the current flowing from the positive ternimal of a battery. The electrons method has it flowing from the negative terminal. What really happens in that the electrons flow from the negative side of the battery (electrons have a negative charge), and current is the flow of electrons. Voltage is like the force which pushes electricity through a wire.

    But you should draw current as flowing from the positive ternimal.

    Short = very low or no resistance
    Open = infinite resistance. No current flow.
  4. Nov 15, 2005 #3


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    Voltage is both push and pull like a clothesline that goes around two pulleys to form a loop. Whether you define it as either or are concerned with the direction of flow is a matter of perspective and ranger gave more information regarding this.

    In an open circuit you have the voltage but since there is no complete path (like the clothesline is broken) no current flows. So it does no work. But in a closed circuit where electricity can flow a complete loop the voltage moves the current along.

    For AC, you could think of putting a battery in one way and then simply reversing it quickly. Extending the clothesline around two pulleys analogy, rather than the clothespin traveling around in an oval as it goes around the pulleys for DC moving it along, instead with AC it just wiggles back and forth. In either example you should (hopefully) see how that you could transfer energy from one pulley to the other pulley.
  5. Nov 27, 2005 #4
    1. Voltage is the potential difference between two points of a circuit. Current is the flow of electrons through a given resistance, set by Ohm's Law formula - I = V/R. Its like water through a tube, The tube is the resistance, the pressure of the water is the voltage, and the water is current. Water will move at a set rate with a given diameter, and given pressure. Increasing the diameter of the tube (lowering the resistance), or increasing the pressure(Uping the voltage) will force more water (current) through the tube. Voltage is the "pressure" driving the current of electrons through a resistance.

    2. The above poster was correct with the notion of two different Current Flow conventions.
    A: Conventional Current - Current flows from Pos >> Neg. Not really what happens but good to trace your circuit out with.
    B: Electron Flow - Current Flows from Neg >>> Pos. This is what really happens in electric DC circuits.

    3. AC means Alternating current, this means the polarity of voltage changes on the source from Pos to Neg to Pos to Neg as a function of Frequency. .-'-.-'-.
    Each time the signal repeats itself in one second is 1 Hertz (Hz), this is its frequency.

    4. A short = Very low resistance connection, like a piece of wire. Remember I = V/R? if the wire has a resistance of .001 Ohms, and has 12 volts across it, thats 12,000Amps, and the heat produced from the Isrq(R) (Current squared times the resistance = power disipated as heat, or 144,000 watts), would pretty much vaporize that wire. All that assuming the source is able to produce 12,000Amp, but doubtful.

    An open = a break in Current, full source voltage can be read across an open (a voltage is a potential difference), but no current will flow. Cut the tube in the voltage example, and place a cap over each end so no water can flow. The pressure is still being put on the end-caps but its not allowing water to move, so there is no current.

    Sry for the long post, i was bored, any corrections will be noted :smile:
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