文档介绍：is the permittivity of free space, measured in farads per meter
The Experimental Law of Coulomb
1. Coulomb's law: the force is proportional to the charge on each and inversely proportional to the square of the distance .
vector form:
3. Example :
Locate a charge of at M(1,2,3) and a charge of
at N(2,0,5) in a vacuum. We desire the force exerted on Q2 by Q1.
Electric Field Intensity
1.
2. Expression in Cartesian Coordinates: For a charge Q at the origin
3. For a charge at the point (not at the origin)
Electric Field Intensity
4. The sum electric field intensity due to two charges:
Electric Field Intensity
5. Example:Find E at P(1,1,1) caused by four identical 3-nC charges located at P1(1,1,0), P2(-1,1,0), P3(-1,-1,0), P4(1,-1,0) as shown in the following Figure.
Field due to a continuous volume charge Distribution
1. Volume charge density ---coulombs per cubic meter(C/cm3)
2. ΔQ in a small volume is:
3. Define volume charge density with a limiting process:
4. The total charge within some finite volume is :
5. The incremental contribution to the E at r produced by an incremental charge ΔQ at r’ is:
Field due to a continuous volume charge Distribution
5. Example:Find the total charge contained in a 2-cm length of the electron beam shown in the Figure below.
Field of a line charge:
1. Assume a straight line charge with a uniform charge density extending along the z axis in a cylindrical coordinate system from -∞ to ∞, shown in the Figure below.
First consider symmetry of the question
With which coordinates the field does not vary
ponents of the field are not present
Field of a line charge:
1. Assume a straight line charge with a uniform charge density extending along the z axis in a cylindrical coordinate system from -∞ to ∞, shown in the Figure below.
Realize that no ponent may vary with Φ
Realize that fields are not functions of z
The field varies only with ρ
2. Other ways of obtaining the inte