# The condition for application of electrostatic theory

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#### Hectoryx

##### Junior Member level 1
The condition for application of electrostatic theory

In the vicinity of antenna, electric field strength have terms that vary as 1/r, 1/(r^2), and 1/(r^3). The terms varying as 1/(r^3) are called the quasi-electrostatic field which can be analyzed with the theory of electrostatic field. The condition is that the size of interested area is less than wavelength/2pi.

My question is that for the frequency of 50MHz, the size must be less than 0.95m according to the theory above. Now there is a big sphere (good dielectric) placed near the antenna. The distance between the bit sphere and the antenna is 0.1m. More important, the diameter of the big sphere is 2m.

Then, if we want to discuss the electric filed distribution, could we use the theory of electrostatic field? If not, what theory should we use? And besides, if we want to use electrostatic filed theory, what is the upper limit of frequency in this condition?

Regards.

Hector

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