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Questions about ground node

  1. Apr 26, 2013 #1
    Is there any current flows from point A to the ground (see the attachment)?

    We use ground node to idicate somewhere in the circuit has ZERO electrical potential. Do we really connect that point to the ground in real world or we just mark that point to make it easier to do calculations?

    Attached Files:

  2. jcsd
  3. Apr 26, 2013 #2


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    Staff: Mentor

    Your second post....Ethanoic.

    There is no current to ground for the components shown. In practice, there can be signal sources that are not shown, they are incidental and usually unwelcome. Example: 50Hz hum induced in that wiring due to proximity to mains wiring, or radio frequencies inducted by nearly or distant stations, or passing taxis with 2-way radios, or motors or car ignitions, or computer chip signals, etc., etc. The earth connection can divert these and render them inconsequential to the operation of your circuit.

    The earth connection may be shared by other circuits, not shown here, but possibly partnering it in some way. It represents a piece of wire, not a connection to terra firma, usually. :smile: Often it's a connection to an area of copper on a circuit board.
  4. Apr 30, 2013 #3
    Are we looking at the same diagram? It looks like a DC current of Vbattey/R would be flowing through the resistor. What am I missing?
  5. May 1, 2013 #4
    In the real world and for this circuit this point - GND - is not needed. SPICE requires a GND node - that is where it starts all of it's calculations from.
  6. May 4, 2013 #5
    The idea of having a surface or conductor with 0 volts (ground) at all points is a useful concept, but in reality, it's best an approximation.
    All practical conductors suffer from resistance and inductance. Thus if current flows between any two points on a conductor, there will be a corresponding voltage drop.
    For this reason, circuit designers separate grounds into different categories:
    * Signal return - For remote instruments or microphones
    * Analog ground - For low current small signal regions
    * Digital ground - Used for micro-controllers and digital circuitry (which tend to have high frequency currents)
    * Power ground - Used to carry high di/dt currents within the power supply regions
    * Chassis ground - Used for safety and as a place to tie down high frequency currents.
    * Safety ground (or neutral) - Used with chassis ground as a means of routing dangerous currents away from users.

    I may not have been complete or given the best description on some of these, but they are the common ones I think about. There's also a slew of work on how you interconnect grounds, and how you deal with noise / offset related issues...
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