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!

I Importance of Current density?

  1. May 31, 2017 #1
    Why we do use electrical current density in place of total electrical current? Actually I want to know what is the advantage of using electrical current density?
  2. jcsd
  3. May 31, 2017 #2


    User Avatar
    Staff Emeritus
    Science Advisor

  4. May 31, 2017 #3
    Yes, I read on wiki article but my question is that why we do use current density which means current/unit area rather than the total current?
  5. Jun 1, 2017 #4


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    We don't always use Current Density. In fact, in many years of EE, Current Density hasn't figured very highly in any of my work. Talk to a power Engineer and you may get a different answer.
    What is the context of your question?
  6. Jun 1, 2017 #5


    Staff: Mentor

    We use whichever one we need for a given problem
  7. Jun 1, 2017 #6
    Current density is a vector, current is a scalar?
  8. Jun 3, 2017 #7
    Current density is a local property (For a point), whereas current is a global property (e.g. for an entire wire). Both are useful depending on the problem but I guess I'll talk a bit more about current density. Densities in general are useful because they allow you to look at the effect of complicated distributions of the quantity in question (e.g. current,charge,mass) by adding up all the little current densities (Numerically or otherwise), current density allows you to find for instance the magnetic field inside a complicated material where only parts of the current have an effect. Another motivation for using densities is that the differential forms of equations, (e.g. Maxwell equations) are more mathematically convenient to work with, and they have to be expressed in terms of local properties.

    Both current and current density are vectors i.e. they both have direction but currents are rarely written in vector form probably because they're written too often and it's assumed obvious
  9. Jun 3, 2017 #8


    User Avatar

    Staff: Mentor

    Current is in fact a scalar. The current through a surface S (e.g. a cross-section of a wire) is defined as $$I = \iint_S \vec J \cdot d\vec S$$ where ##\vec J## is the current density at each point on the surface and ##d \vec S## is the infinitesimal surface element at that point.
  10. Jun 3, 2017 #9


    User Avatar
    Science Advisor
    Gold Member

    Perhaps an example would help: You can't make any progress on eddy currents without solving for the spatially varying current density.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted