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How does battery maintain potential differece meaning behind it & why is it grounded

  1. Nov 7, 2009 #1
     

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  3. Nov 8, 2009 #2

    Dale

    Staff: Mentor

    Re: how does battery maintain potential differece meaning behind it & why is it groun

    The battery has some chemical reaction that pushes the electrons from the - terminal to the + terminal with a specific amount of energy. This amount of energy per electron is a voltage or in other words a potential difference.
     
  4. Nov 8, 2009 #3
    Re: how does battery maintain potential differece meaning behind it & why is it groun

    i know that but in many books its written the plate is maintained at postitive potential
    a battery is connected so that it sets up a potential difference

    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

    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
     
  5. Nov 8, 2009 #4

    Dale

    Staff: Mentor

    Re: how does battery maintain potential differece meaning behind it & why is it groun

    That is not exactly correct. If the negative terminal is grounded (0 Volts by definition) then the positive terminal will have a positive potential. But you could just as easily ground the positive terminal in which case the negative terminal would have a negative voltage of the same magnitude as the positive terminal did previously. It really is a potential difference that a battery supplies.
    Which figure? You have three figures showing two completely different kinds of devices.
    I don't know what he meant by this. Electromagnetism has no range limitation, although the field of a point charge falls off as 1/r². It gets weaker over distance, but it never stops.
     
  6. Nov 8, 2009 #5
    Re: how does battery maintain potential differece meaning behind it & why is it groun

    That is not exactly correct. If the negative terminal is grounded (0 Volts by definition) then the positive terminal will have a positive potential. But you could just as easily ground the positive terminal in which case the negative terminal would have a negative voltage of the same magnitude as the positive terminal did previously. It really is a potential difference that a battery supplies.

    thats what i want to know the meaning behind what u have stated above (physical meaning like previously u told that voltage is energy gained or lost by unit charge)

    "The battery has some chemical reaction that pushes the electrons from the - terminal to the + terminal with a specific amount of energy. This amount of energy per electron is a voltage or in other words a potential difference." the electron has higher energy at one site and 0 energy at the other.

    like that i also what the meaning of what



    Which figure? You have three figures showing two completely different kinds of devices.I don't know what he meant by this. Electromagnetism has no range limitation, although the field of a point charge falls off as 1/r². It gets weaker over distance, but it never stops.
    first i was referring to discharge tube
    next i wanted u to explain the role of battery in van de graff
     
  7. Nov 9, 2009 #6

    Dale

    Staff: Mentor

    Re: how does battery maintain potential differece meaning behind it & why is it groun

    OK, so basically a battery does work on an electron as it moves it from the + terminal to the - terminal. For example, in a car battery the chemical reactions do 12 eV of work on each electron resulting in a potential energy increase of 12 Joules for every Coulomb of electrons moved from the + to the - terminal. Or 12 Joules/Coulomb is 12 Volts.

    The ground is just an arbitrary place that you call 0 Volts. In other words, you set your potential energy at ground equal to 0. This is completely analogous to the fact that if you are working a problem involving gravitational potential energy (mgh) you can set your h=0 point anywhere you want.

    I don't really know anything about van de graff generators, but I will try to answer about cathode ray tubes. Basically, you heat up the cathode until it is so hot that electrons begin to boil off the surface. Then, if you have negatively charged the cathode and positively charged the anode then the electrons will be repeled from the cathode and attracted to the anode by Coulombs law. They will accelerate gaining kinetic energy (measured in eV) equal to the potential difference (measured in V) between the anode and cathode.
     
    Last edited: Nov 10, 2009
  8. Nov 11, 2009 #7
    Re: how does battery maintain potential differece meaning behind it & why is it groun

    OK, so basically a battery does work on an electron as it moves it from the + terminal to the - terminal. For example, in a car battery the chemical reactions do 12 eV of work on each electron resulting in a potential energy increase of 12 Joules for every Coulomb of electrons moved from the + to the - terminal. Or 12 Joules/Coulomb is 12 Volts.

    The ground is just an arbitrary place that you call 0 Volts. In other words, you set your potential energy at ground equal to 0. This is completely analogous to the fact that if you are working a problem involving gravitational potential energy (mgh) you can set your h=0 point anywhere you want.

    i almost 99.9%got it
    the one doubt that i have is in electronics the negative terminal is grounded which means according to u negative terminal is 0 volts
    the grounding of - terminal is a way of representation of an arbitrary place that you call 0 Volts in this case u connect it with - terminal to show that - terminal is at 0 volts that is the unit charge has no energy at 0 volts
    am i right did u get to my point?
     
  9. Nov 11, 2009 #8

    Dale

    Staff: Mentor

    Re: how does battery maintain potential differece meaning behind it & why is it groun

    Yes, that is correct.
     
  10. Nov 12, 2009 #9
  11. Nov 13, 2009 #10

    Dale

    Staff: Mentor

    Re: how does battery maintain potential differece meaning behind it & why is it groun

    That is this thread and I responded :frown:
     
  12. Nov 13, 2009 #11
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