see the attachment
1) plz explain the function of battery and ground in the picture (discharge tube)
my doubt was that in discharge tubes the 2 plates are connected to some voltage source
let it be battery for instance see the fig in this case between the two plates there is empty space then what does the battery here do
does it send electrons to cathode which deposits on it and the cathde induces +charge on the anode and electrons return back
that is my doubt am i right or wrong
but when i consulted my physics teacher he told me that it cant induce to such long distances , he told that what happens is that electrons in anode are attracted by +terminal of the battery and when they reach the +terminal they repel the electrons in the - terminal which goes to the cathode as a result of repulsion

2)my main doubt is what is the meaning that battery maintains potential difference i cant understand this term can any1 explain in terms of charge movement (not mathematical)


3) also i read in
http://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.html
about ground reservoir analogy i cant understand these lines

THE GROUND PROVIDES REFERRENCE VOLTAGE.THE GROUND CAN SUPPLY CHARGE TO CIRCUIT BUT ITS MAIN FUCTION IS TO HOLD THE VOLTAGE OF NEARBY WIRES AT THE VOLTAGE OF EARTH
PLZ ELECTRICAL ENGINEERS PLZ GUIDE ME

4) also why is that - terminal of battery is grounded in van de graff
in van de graff current cant flow from battery since it is not open circuit
in many cases circuits will not be complete as in discharge tube vaccuum tube.In these cases battery cant supply current then what else it does
if u answer it maintains potential differece plz tell me the meaning of it and plz explain about my grounding doubt as mentioned in this same quote

plz answer all my questions that i have numbered

 

The first picture shows a thermionic tube in which electrons (negative charge carriers) given off by the heated cathode are attracted towards the positive anode.

You may be confused by the arrow showing current flow coming out of the battery to the anode. In fact, the flow of electrons carries on from the anode to the battery.

The arrow shows "conventional" current flow from positive to negative when, in fact, electrons flow from negative to positive.

The third diagram "Gas Discharge Tube" shows the same thing. "Cathode Rays" are a stream of electrons. In this diagram, the cathode is not heated and the electrons are pulled off the cathode by using a much higher voltage between cathode and anode.

In the above, the ground connection is not shown and does not matter.

The second diagram shows a Van de Graph Generator used to make a very high positive voltage. A source of ions - which are POSITIVE charge carriers (actually atoms that are short of electrons) are attracted to ground which is negative with respect to the source. It actually does not matter where ground is connected. This will work just the same if the ion source was at ground and the target was connected to a high negative voltage.

So the ground is often used as a reference but is does not matter where it is connected.