# Propagation

## Electric Field

- An
**electric field** is the force resulting from electric charges
**Field strength** is measured in **volts/meter (V/m)**,
and is **inversely proportional** to distance from the source, i.e.
at twice the distance the field strength is halved
- Field strength may also be expressed as
**Power Density** in
**Watts/meter**^{2} (W/m^{2}).
Power Density is proportional to the **inverse of the square of the distance**
from the source, i.e. as twice the distance power density is a quarter