## Field Quantities

- E
- Electrical field intensity (V/m).
- Defined as the electric force on a unit charge. Only vector needed in
discussing electrostatics (effects of stationary electric charge) in
free space.
- D
- Electric flux density or electric displacement (C/m2).
- Useful in the study of electric field in material media.
- B
- Magnetic flux density (T, Tesla, V-sec/m2).
- Magnetic force acting on a charge moving with a given velocity. Only
vector is needed in discussing magneto statics (effects of steady
electric currents) in free space.
- H
- Magnetic field intensity (A/m).
- Useful in the study of magnetic field in material media.

## Universal Constants in Free Space

$$c\text{\hspace{0.17em}}=\text{\hspace{0.17em}}\frac{1}{\sqrt{{\epsilon}_{0}{\mu}_{0}}}\text{\hspace{0.33em}}\text{m/s}$$

Or,

${\epsilon}_{0}\text{\hspace{0.17em}}=\text{\hspace{0.17em}}1\text{\hspace{0.17em}}/\text{\hspace{0.17em}}\left({c}^{2}{\mu}_{0}\right)$

$\approx \text{\hspace{0.17em}}{\left(1\text{\hspace{0.17em}}/\text{\hspace{0.17em}}36\pi \right)}^{\prime}\text{\hspace{0.17em}}{10}^{-9}\text{\hspace{0.33em}}\text{F/m}$

Where,

- $c$
- Velocity of electromagnetic wave (including light).
- $c\text{\hspace{0.17em}}\approx \text{\hspace{0.17em}}{3}^{\prime}{10}^{8}\text{\hspace{0.33em}}\text{m/s}$
- ${\epsilon}_{0}$
- Permittivity of free space.
- $D\text{\hspace{0.17em}}=\text{\hspace{0.17em}}{\epsilon}_{0}E$
- ${\mu}_{0}$
- Permeability of free space.
- $H\text{\hspace{0.17em}}=\text{\hspace{0.17em}}\left(1\text{\hspace{0.17em}}/\text{\hspace{0.17em}}{\mu}_{0}\right)\text{\hspace{0.17em}}B,\text{\hspace{1em}}{\mu}_{0}\text{\hspace{0.17em}}=\text{\hspace{0.17em}}4{\pi}^{\prime}{10}^{-7}\text{\hspace{0.33em}}\text{H/m}$

${\epsilon}_{0}$
and
${\mu}_{0}$
are not independent.