Monday, November 19, 2012

Continuous Charge Distribution

On the surface of a charged conductor, it is impractical to specify the charge distribution in terms of the locations of the microscopic charged constituents. It is more feasible to consider an area element DS .On the surface of the conductor (which is very small on the macroscopic scale but big enough to include a very large number of electrons) and specify the charge DQ on that element. We then define a surface charge density s at the area element by
We can do this at different points on the conductor and thus arrive at a continuous function s, called the surface charge density. The units for sare C/m2.

Similar considerations apply for a line charge distribution and a volume charge distribution. The linear charge density l of a wire is defined by

where Dl is a small line element of wire on the macroscopic scale that, however, includes a large number of microscopic charged constituents, and DQ is the charge contained in that line element. The unit of linear charge density (l) is C/m.

The volume charge density (sometimes simply called charge density) is defined in a similar manner:

where DQ is the charge included in the macroscopically small volume element DV that includes a large number of microscopic charged constituents. The unit for volume charge density r is C/m3.


Some of these questions which may be asked in your Board Examination 2012-2013

Q1: When a plastic comb is passed through dry hair, what type of charge is acquire by comb?

Q2: Does motion of a body affect its charge?

Q3: What is the origin of frictional forces?

Answer these questions in comment box and help your friends


  1. 1.ans: -ve charge
    2.ans: No
    3.ans: I think frictional forces are developed by rubbing two insulating bodies

  2. No derivation . Oh !!!!!