Phys 4, Section
2
Feb 20, 2002
Magnetic Field of a Moving Charge
Experiments show that the magnetic field of of moving charge can be expressed
as:
μ_{o} ≡ 4π ×
10^{7} N·s^{2}/C^{2} is called the permeability
of free space. The constant ε_{o}
that is used in electric field calculations is called the permittivity of
free space. Note that ε_{o}μ_{o}
= 1/c^{2}.
Example:
Two protons with a vertical displacement of r between them move in the
xy plane parallel to the xaxis at the same speed v (small compared to c).
When they are both at x = 0, what is the ratio of the electric/magnetic
forces between them?
F_{E} = kq^{2}/r^{2}
To get F_{B} acting on top charge, first find B caused by bottom
charge:
So, the force this field exerts on the top charge is:
Comparing the ratio of F_{B} to F_{E}:
Last modified on February 27, 2002
