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Where do electrons go?

  1. Aug 5, 2010 #1
    I have a couple of questions:

    1]If we connect +ve terminal of DC battery to a bulb(using one wire) & another wire coming out from bulb is inserted in ground(earth) instead of connecting it to the -ve terminal of battery, will bulb glow? if yes, does it mean electrons in the wire flow into the earth? and how can bulb glow if electrons don't return to its source?

    If same thing is done with AC power supply do electrons moving out of the wire(where it is inserted in ground) into the ground & entering back in the wire as in AC, electrons move back & forth?

    my assumption is electricity is generated when electrons flow from source through the wire and come back to the source again. but how then grounding wire carries the current as it end in the ground?

    2]We receive 1-phase AC voltage at home. AC polarity changes per complete cycle. But if we insert electrical tester in the wall socket, it's only one hole(live) in which tester light glows, in other hole(neutral) it doesn't.
    But since the polarity changes(each hole becomes +ve and -ve alternately) in
    other(neutral) hole also, tester light should glow, but it doesn't. Why?
     
  2. jcsd
  3. Aug 5, 2010 #2
    In most systems the ground is connected to 0 volts. That is how we set them up. When you send electricity to the light and then to the ground, it goes from the ground back to the power supply. Both the power supply and the light have their refrence of 0 volts connected through the ground. So in this case the electricity flows through the ground to complete the circuit. It is not uncomon to have current running through your ground. It is just another part of the curcuit.
    As for the socket, 110 have a hot, a common, and prehaps a ground. The hot is where the power sent through. The common is generally held at ground and is used to complete the circuit.
     
  4. Aug 5, 2010 #3

    sophiecentaur

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    @x+iy
    A mains tester works because the potential difference between the live and Earth makes a very small (imperceptible) current flow through the tester and your body to Earth. This current is just enough to light the neon. When you stick it in the Neutral socket, the potential difference (just a volt or two, usually) is not enough to give sufficient current to light the neon.

    @kgbgru
    "The hot is where the power sent through."
    This is a bit misleading because the power flow involves Both live and neutral conductors. Their PD relative to the rest of the world is irrelevant; the same current flows through each one and there is a Potential Difference between them..
     
  5. Aug 5, 2010 #4
    @sophiecentaur

    "@x+iy
    A mains tester works because the potential difference between the live and Earth makes a very small (imperceptible) current flow through the tester and your body to Earth. This current is just enough to light the neon. When you stick it in the Neutral socket, the potential difference (just a volt or two, usually) is not enough to give sufficient current to light the neon."

    Thanks for the quick reply. I have couple of more questions.

    When the tester light glows, does it mean electrons flow like,from live terminal > tester > body > floor & walls of building > inside the earth in one half cycle and then take the same path back from earth in next half cycle? But how the circuit is completed because current seems to be flowing in straight line and not in a circle(close circuit), as electrons need to come back to source for current to flow.
    (do electrons actually jump form end of the wire into the earth in 1st half cycle and again like sucked into wire from earth into wire in next half cycle?)

    Also, as you say PD between neutral and earth is not enough to make electrons flow. But since the polarity changes in AC, then neutral should become live (or does it?) live become neutral. Then PD between neutral and ground should become equal to that of between live and earth.

    Sorry,i am making it too long, but i want to let you know what exactly my concept.
    I am really confused about this, please help!!
     
  6. Aug 5, 2010 #5

    sophiecentaur

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    A few points should clear this up for you.
    1. Your idea of a flow round a circuit is incomplete. The current 'loop' goes back to the generator, via earth or neutral conductor. Out there, somewhere, Neutral and Earth are connected together. So you have, in effect, a huge loop of circuit.

    2. When a current flows, the electrons flow VERY slowly - a few mm per second - so, for AC, they are just moving backwards and forwards by less than a mm. Remember, there are a LOT of them - one per atom is available to move in a metal. The energy is transferred is the net charge flow (Current) times the Voltage. I use the bicycle chain as an analogy; however long the chain is, the power gets to the other end just as quickly (the only difference in the delay involved is due to the speed of the impulse in the tension on the chain when you first stamp down on the pedal).

    3. The Voltage on the Live wire oscillates from +V to -V (relative to earth), going through zero. The voltage on the neutral stays more or less the same at zero. In many ways, the Earth / Neutral thing is irrelevant. You could quite easily connect the neutral and Earth wires together at the point where they enter the house so you could effectively call the neutral 'Earth'. The reason for using a neutral wire involves the next level of engineering sophistication and you can ignore it for a start.
     
  7. Aug 5, 2010 #6
    @sophiecentaur

    Thanks a lot. That really cleared my confusion.
     
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