Formula for electric field for capacitor and cylinder

AI Thread Summary
The discussion centers on the derivation of electric field formulas for a parallel plate capacitor and a cylindrical capacitor. The formula for the parallel plate capacitor is E = k(2πq/A), while for the cylinder, it is E = k(q/(2Lr)). These formulas are derived from the electric displacement field, D, which relates to surface charge density as D = q/A for the parallel plate and D = q/(2πrL) for the cylinder. Understanding these relationships helps clarify the origin of the electric field equations provided by the professor. This foundational knowledge is essential for grasping electrostatics in capacitors.
derek181
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My prof gave two formulas without much explanation as to where he got them from. For a parallel plate capacitor he gave it as E=k2∏q/A and for a cylinder he gave E=kq2/Lr where L is the length of the cylinder and r is the radius and A is the area. Can someone please explain how he derived these.
 
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hi derek181! :smile:

he gets it from the electric displacement field, D, which is always equal to the surface charge density, ie charge/area …

D = q/A or D = q/2πrL :wink:​


(and see here)
 
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