When we calculate the electric field using this equation, the result is as follows.
Literal
This equation [by-によって] electric-field [obj-を] calculate-[and-てやると], result [topic-は] next [gen-の] like become.
電場 'electric field' is a physics compound. ~によって 'by means of' marks the equation as the instrument. ~してやると uses やる in its explanatory/procedural sense (common in scientific writing) — 'if we go ahead and calculate,' not the benefactive 'do for someone.' 次のようになる 'becomes like the following' is the standard academic transition phrase introducing a result.