Electric field strength is a measure of the strength of the force exerted on an electron by an electric charge. There are three types of electric fields in matter: static, electromagnetic, and electrostatic. In general, electrostatic fields apply in insulators where the electric charges cannot easily move from one area to another or between conductors. Magnetic fields can be thought of as being created by moving charges with currents and tend to replace electrostatic ones when there is motion in a medium.
Static Electric Field Strength
The magnitude of this type of field is given by the Coulomb constant c; 1 J / C 2
In a vacuum outside charged particles have zero orbit radius so this magnitude can be calculated using simple geometry: 0 . 1 2 R e q r e where R e = 6 . 3 × 10 8 m is the radius of the earth and r e q = 1 . 6 × 10 9 C is the charge of the electron. Thus, at some point in space to the right of figure 4, as shown in figure 2, which has been labeled A, E s t a t = 5 . 9 × 10 8 N / C 2
Magnetic field strength is given by B=μ0nI/2πr3 where μ0 is the permeability of free space, 4⋅10−7 N/A2; n is the number density of charge carriers (e.g. free electrons and ions) in the material; I is the current, it is generally assumed that this current stays constant through body of a conductive material; and r is a vector perpendicular to the plane containing the cardinal axes of an object where μ0, n and I satisfy B=μ0nI/2πr3. The formula also works for a magnetic field applied to an object of uniform cross-sectional thickness and has been used to calculate the magnetic field produced by a current in the body of an insulator.
In simple situations, such as conductive copper wire, B is the vector sum of E1 and E2: B = μ 0 n 1 I 2 π r 3 . Here, μ0=4⋅10−7 N/A2 and n 1 =1.6×10 9 C. The E1 field is always perpendicular to the wire, so it is cancelled in B and E2 is the unknown. E2 has units of J/m and is repeated in equation (1).
Electrostatic Field Strength
The magnitude of this type of field is given by the dielectric constant ε, commonly called relative permittivity. Electrostatic fields also exist in conductive media due to the electric polarization of charge carriers. The magnitude of this field is given by the magnitude of the charge separation Δ”Q” and is given by Coulomb’s Law:
D + D = −ΔQ/ε0 ε r e q r e . Given that Δ”Q”=4×10 C and ε=8.895×10−12 F/m, then, E s t = 2 . 4 × 10 4 N / C 2
In a vacuum outside charged particles have zero orbit radius so this magnitude can be calculated using simple geometry: 0 . 1 2 { R e q r e i = −6 . 3 × 10 8 m } where R e q = 1 . 6 × 10 9 C is the radius of the earth and r e q = 1 . 6 × 10 9 C is the charge of the electron. Therefore, at some point in space to the left of figure 4, as shown in figure 1, which has been labeled B, E s t a t = 9 . 8 × 10 8 N / C 2
Electrostatic fields also exist in conductive media due to electric polarization of charge carriers. The magnitude of this field is given by the magnitude of the electric field, ε, which can be calculated from Gauss’ Law, Coulomb’s Law and Ampere’s Law.
I + I = ε E s t where I = 2 π r e q C . Solving (2) in terms of E we get E s t = 4 . 9 × 10 8 N / C 2
Electrostatic fields also exist in conductive media due to electric polarization of charge carriers.
