Dear sir,The electric field will change vectorially in a wire of non uniform cross section - that is understood. But the magnitude of electric field is potential difference divided by lenght . How would that change? Why should the magnitude of electric field change at all?

Dear student 

Electric field strength is a quantitative expression of the intensity of an electric field at a particular location. The standard unit is the volt per meter (v/m ) The field strength at a particular distance from an object is directly proportional to the electric charge, in coulombs, on that object.

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