DC Circuits

Discussion in 'Homework Help' started by twocorp, May 6, 2010.

  1. twocorp

    Thread Starter New Member

    May 6, 2010
    Thank you for providing this fantastic opportunity to all and sundry, we greatly appreciate it. However, I do have a couple of basic queries :

    1) In the book , you mention conventional flow verus actual electron flow -- one of the hardest things that we beginners have trouble understanding is the layout of components in electrical diagrammes, ie
    on your page 94, if the flow of electrons is from negative to positive, why aren't the disconnect switch and the on/off switch between the negative side of the battery and the load ?

    2) The other thing that is difficult to understand is the use of the 'earth'. You don't actually say how this works...ie on p94 diagramme 1, why isn't the voltage / current split between the earth wire and the wire to the load ?

    Thank you
  2. mik3

    Senior Member

    Feb 4, 2008
    It doesn't matter where you connect the switch in a simple circuit because electrons will stop flowing wherever you brake the circuit.

    However, in grounded systems it is important to brake the circuit in the positive power supply side (live wire in AC). This is because the user assumes that he cannot get shocked if the circuit is switched off because the negative side (neutral in AC) of the power supply is grounded. However, if the switch is placed on the negative wire and the circuit is switched off, electrons will stop flowing but the ungrounded positive wire will be connected on the load. Thus, if the user touches the load he will get shocked.

    The earth, under normal conditions, does not carry any current. Therefore, the current is flowing only through the load wires. If, by accident, a live wire touches a metallic frame which is earthed then current will flow through the earth wire.
  3. twocorp

    Thread Starter New Member

    May 6, 2010
    Thank you very, very much indeed !
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    And welcome to AAC.

    You may want to look into SINKING and SOURCING current.

    They will show you how current is supplied to different circuits or devices.

    Sinking current is AFTER the flow goes through a device, the switch is on the ground side. So you are sinking the current that went through the device to ground.

    Sourcing is SUPPLYING. So the switch is on the hot side, and is a source of current BEFORE the device.