How things work college course/Electricity and Field theory

For an introduction to the purpose and scope of this work see Talk:How_things_work_college_course/Electricity_and_Field_theory


Region b is neutral because 4 lines enter and 4 lines leave. The field at d is stronger than the field at e because the field lines are closer together at d, but the field at e is more uniform because the field lines are nearly uniform.
Region b is negative because 4 lines enter, while 3 lines leave.
Region b is positive because 4 lines enter, while 5 lines leave.
Electricity is the motion of charged particles (usually electrons)
Electrons have potential energy due to electric forces. Potential energy is associated with these forces, and the fact that energy is involved that makes electricity useful.
To understand energy we we need to introduce the concept of fields.
Wind velocity and air temperature are defined on Earth's atmosphere.
Three other important fields are electric potential, electric field, and magnetic field. The first two can be defined by analogy with gravity.
There are two ways to visually represent vector fields: A spatial distribution of vectors, and field lines.
The most common way to represent a scalar field is the use of contours.
The gravitationa analogy (first of two analogies)
F = mg like F=qE
PE = Fd if force is uniform and parallel to displacement
PEG = m(gh) = mφ, where φ=gh is gravitational potential.
PE = qEd = q(Ed), where V=Ed is gravitational potential (replace h=height by d=distance)
Inverse square
(advanced sum over sources)
Electric fields are rarely uniform. Need examples