1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Potential Difference between earth and battery

  1. Sep 7, 2015 #1
    When I connected the positive terminal of the battery to one terminal of the bulb and the other terminal (of the bulb)to the ground the bulb did not glow, even when a potential difference exists?
     
    Last edited: Sep 7, 2015
  2. jcsd
  3. Sep 7, 2015 #2

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    I don't know what actual circuit you were using but the - on your battery needs to have a continuous connection to Earth. The Earth has to complete the circuit. Check the connections. (Try it with just a negative' wire first, to check battery, bulb and holder.)
     
  4. Sep 7, 2015 #3

    davenn

    User Avatar
    Science Advisor
    Gold Member

    Im presuming ( from your description) this is your setup ...

    cct.GIF

    you have a hole in the circuit ... the other side of the light bulb isn't connected to anything
    Yes, there is a potential difference between the other terminal of the light bulb and the ground,
    but the air resistance is VERY high ( a very good insulator). The breakdown voltage of air is at least
    5000V / cm possibly higher ( someone will confirm)

    Dave
     
    Last edited: Sep 7, 2015
  5. Sep 7, 2015 #4
    No this is not my circuit , the negative side of the bulb is connected to the ground instead of the negative terminal of the battery
     
  6. Sep 7, 2015 #5

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    If you don't connect bulb and battery to Earth then how is there a complete circuit`??
    Left to its own devices, the positive terminal of the battery will be pulled to Earth potential and the negative terminal will find itself at -battery volts.
     
  7. Sep 7, 2015 #6

    Dale

    Staff: Mentor

    There is no potential difference across the bulb. Why should the bulb care if there is a potential difference somewhere else?
     
  8. Sep 7, 2015 #7

    davenn

    User Avatar
    Science Advisor
    Gold Member

    This .... ?
    cct1.GIF
    If not that, where does the negative terminal of the battery go to then ?

    You may now realise how unclear your original description was


    Dave
     
    Last edited: Sep 7, 2015
  9. Sep 7, 2015 #8

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Everyone with a question about circuits should do us the courtesy of giving some sort of a labelled diagram.
     
  10. Sep 7, 2015 #9

    davenn

    User Avatar
    Science Advisor
    Gold Member

    indeed
     
  11. Sep 7, 2015 #10

    ogg

    User Avatar

    Electrons from the battery need to return to the battery, or within microseconds a charge imbalance will stop any more electrons from flowing. Electricity flows from the battery back into the battery, there is no loss or gain of electrons in the batter or in the lightbulb (ignoring that first microsecond). Wire is a good conductor, which means that it will allow current to flow with little resistance. In a good conductor like wire, current flow is ONE WAY. To be clear: the direction current can flow in a wire can change, but at any one time current only flows in one direction. This means that if you connect a light bulb to one terminal of a battery, you aren't going to see anything happen. Only when you connect the other terminal of the battery to the other part of the lightbulb (so that current flows through the filament (assuming its incandescent)) and so that the electrons can go in on one wire and go out on the other at the same time will it light up.
     
  12. Sep 11, 2015 #11

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    There is no potential difference across the bulb. You appear to be assuming that the -ve terminal of the battery is at 0V with respect to ground. That's a mistake.

    Lets say it's a 9v battery. The +ve terminal is connected to ground via the bulb. The -ve terminal of the battery is not connected to anything so it will be at roughly -9V (minus nine volts) with respect to ground. This is because the resistance of the bulb is much lower than the resistance of the open circuit on the -ve terminal.
     
  13. Sep 11, 2015 #12

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    Perhaps consider a 9V battery still isolated in it's packaging. The -ve terminal is not necessarily at 0V with respect to ground. All you can really say is that the +ve terminal is +9V with respect to the -ve terminal. You can't be sure the +ve terminal is 9V with respect to ground until the -ve terminal is connected to ground.
     
  14. Sep 11, 2015 #13

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    If this is proving difficult to the OP then why not reiterate the old, elementary rule which we learn in School 'You have to have a complete circuit'. Start with that and stick with it when trying to figure things out. The idea of Potential and Potential Difference involves a higher level of thinking.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Potential Difference between earth and battery
Loading...