1. Download free Tapatalk for iPhone or Tapatalk for Android for your phone and follow the SDN forums with push notifications.
    Dismiss Notice
Dismiss Notice

Interview Feedback: Visit Interview Feedback to view and submit interview information.

Interviewing Masterclass: Free masterclass on interviewing from SDN and Medical College of Georgia

Dismiss Notice
Hey Texans—join us for a DFW meetup! Click here to learn more.

question about insulators and voltage

Discussion in 'MCAT Study Question Q&A' started by zebalong, Dec 10, 2008.

  1. zebalong

    10+ Year Member

    Joined:
    Sep 24, 2007
    Messages:
    524
    Likes Received:
    28
    Status:
    Resident [Any Field]
    the question is from TPR ICC and for some reason it is just not clicking:

    Before lightening strikes air between the a cloud and a ground acts as an insulator, what describes the effect of the air?

    The answer is basically that air reduces the potential difference between the cloud and the ground...

    I know Q=VC so as C increases (bc of the air) V decreases? (im assuming potential difference is Voltage.. )

    Also can someone explain why when an electron travels from a thundercloud to the ground it causes a decrease in potential energy as it moves toward a region of higher electric potential... i just can't seem to comprehend something decreasing PE by moving to a higher electric potential... seems so counter intuitive
     
  2. Note: SDN Members do not see this ad.

  3. BerkReviewTeach

    BerkReviewTeach Company Rep & Bad Singer
    Exhibitor 10+ Year Member

    Joined:
    May 25, 2007
    Messages:
    3,842
    Likes Received:
    603
    I think it's easiest to start by thinking about what an insulator does. In a simplified perspective, an insulator does not allow for charges to travel from one point to another. Air cannot stabilize charges, so it does not want a charge jumping from one molecule to another. Hence, charges do not flow well through air, so air is said to be an insulator.

    In the case of the cloud, the electrons accrue in the cloud and it builds up a bigger and bigger magnitude of charge (Q). Eventually the repulsion of the charges within the cloud or the attaction to the electron poor ground will cause an electron to fly off and head for the ground. Anytime there is a "better place" for a charged species such as an electron, there is a "potential" for the charged species to move there.

    As far the change in potential compared to potential energy change, you have been screwed over by physics convention. Potential difference, as it is defined in physics, is based on the potential movement of POSITIVE charge. Field lines and potential differences are based on how a positive charge would migrate. Positive charges naturally flow from regions of higher potential to regions of lower potential. However, because an electron is negatively charged, it naturally travels from a point of lower potential to a point of higher potential. For an electron, going from a region of "lower potential" to a region of "higher potential" is favorable, so it converts its stored electrical potential energy into kinetic energy. Basically qEdeltad = 0.5mvexp2.
     
  4. zebalong

    10+ Year Member

    Joined:
    Sep 24, 2007
    Messages:
    524
    Likes Received:
    28
    Status:
    Resident [Any Field]
    thanks! :D i get it.. at least in at the moment
     

Share This Page