Tham khảo tài liệu 'chapter 6 experimental mapping methods', khoa học tự nhiên, vật lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 6 EXPERIMENTAL MAPPING METHODS We have seen in the last few chapters that the potential is the gateway to any information we desire about the electrostatic field at a point. The path is straight and travel on it is easy in whichever direction we wish to go. The electric field intensity may be found from the potential by the gradient operation which is a differentiation and the electric field intensity may then be used to find the electric flux density by multiplying by the permittivity. The divergence of the flux density again a differentiation gives the volume charge density and the surface charge density on any conductors in the field is quickly found by evaluating the flux density at the surface. Our boundary conditions show that it must be normal to such a surface. Integration is still required if we need more information than the value of a field or charge density at a point. Finding the total charge on a conductor the total energy stored in an electrostatic field or a capacitance or resistance value are examples of such problems each requiring an integration. These integrations cannot generally be avoided no matter how extensive our knowledge of field theory becomes and indeed we should find that the greater this knowledge becomes the more integrals we should wish to evaluate. Potential can do one important thing for US and that is to quickly and easily furnish US with the quantity we must integrate. Our goal then is to find the potential first. This cannot be done in terms of a charge configuration in a practical problem because no one is kind enough to 169 I e-Text Main Menu Textbook Table of Contents 170 ENGINEERING ELECTROMAGNETICS tell us exactly how the charges are distributed. Instead we are usually given several conducting objects or conducting boundaries and the potential difference between them. Unless we happen to recognize the boundary surfaces as belonging to a simple problem we have already disposed of we can do little now and must wait
