xiv:
Re,
Sorry for my late responde and Thanks a lot for your answers.
So, If I understand, the GND is the reference point of the circuit to measure voltages on a circuit and the use of the negative terminal of a battery to talk of GND it is just to simplify the thing ?
It is a reference point. Just like if you want to make your home a reference point on a map --- from which other places (distance and angle etc) on the map can be located (in relation to your home location). And ---- if the reference point on the map is changed to a new reference point .... such as somebody else's home, then that's ok too. No matter which reference point you choose to be the 'reference point' (or origin, or zero location) .......... it will still be possible to work with the system.
Circuit diagrams are like that too. You don't necessarily need to choose the reference point on the circuit to be at a negative terminal of a voltage source, or you don't necessarily need to choose the reference point to be at a spot where the largest number of wires (lines or branches) are connected to. But there can be 'benefits' or advantages in choosing a particular point (node) in a circuit to be a reference (GND) point -------- advantage for circuit analysis (for example).
That is - to analyse a circuit, or to design a circuit, some equations involving Ohm's law, Kirchoff's laws etc are used. And a reference point (node) on the circuit is chosen to conveniently do the circuit analysis. And the reference point is generally and arbitrarily assigned to be zero volt (for convenience). It doesn't have to be assigned 0 volt though. But is usually convenient to be assigned to 0 volt. And we can just give this reference point a name ----- eg. GND.
Also ----- dual polarity circuits (with +Vcc and -Vcc supplies) often have the GND 'assigned' to be half-way between +Vcc and -Vcc, which is 0 volt. And when the two identical voltage supplies are connected up in regular 'series' fashion, with the GND ('zero' voltage) point is arbitrarily assigned to be half-way between +Vcc and -Vcc .......... it will turn out that the lowest voltage potential will not be 0 volt. Instead, the lowest potential in that particular circuit (with that selected GND point) would be **-**Vcc.
And also ----- on a circuit diagram, the GND node is often assigned a symbol ---- just so that we can identify that node. And people often use the earth symbol for that. The earth symbol can just be treated as a symbol. It does NOT mean that current or power flows into that symbol. In general, after using the symbol to identify that GND symbol (label) ....... just treat that symbol like an open circuit (infinite resistance, infinite impedance) ..... or pretend that it's not even there (even though it is there for identification) for circuit analysis purposes.
We also keep in mind that some circuits incorporate electrical safety systems that involve GND as part of the electrical safety circuitry. But can always read up on that sort of thing later (eg. google 'ground and electrical safety').
In the two circuits below ....... the GND node has just been assigned to different nodes. But - as mentioned, for circuit analysis, the voltage difference across the 1000 ohm resistor is still going to be 24 volt. And the circuit analysis result will provide consistently the current flowing through the resistor (with the arrow providing a reference direction too) being 0.024 A.
Note ---- in the left-hand circuit, the lowest voltage in that circuit will be -12 volt relative to GND. And in the right-hand circuit, the lowest voltage in that circuit will be 0 volt (relative to GND). And 'GND' is very typically assigned a voltage of zero volt. That is, the voltage of 'GND' relative to ITSELF is zero volt.
) Or a ladder could be in outer space where there is no meaningful relationship to ground or earth.
