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!

Homework Help: Volumetric Charge Density

  1. Apr 1, 2010 #1
    1. The problem statement, all variables and given/known data
    If the Earth's surface was charged to QTOTAL = 13548.3 [C] by removing all of the electrons from a volume of soil, how large would this volume be? Assume electron density of soil = 7e23 [cm-3].

    2. Relevant equations
    Volumetric charge density pv = QTOTAL/volume of soil.

    Electron density is = # of electrons per unit volume.

    3. The attempt at a solution
    By rearranging the volumetric charge density formula, I can gather that QTOTAL / pv. Rearranging the second formula, I can get volume equal to #electrons/electron density. In a general sense, density is equal to mass/volume. I could solve for volume easily here, knowing the mass of an electron. But then, how is charge involved? How do I get the volume of soil, given the amount of charge that was removed from this volume?

    Thank you for the help!
  2. jcsd
  3. Apr 1, 2010 #2


    User Avatar
    Homework Helper

    No mass is involved in this problem. You have charge, charged particles (electrons) and their density. You know the charge of an electron. Knowing the electron density (number of electrons in 1 cm-3), calculate the charge density. From the total charge and charge density, you get the volume.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook