Electromagnetic theory is essentially a study of some particular field. We define a field

as a function which specifies a particular quantity everywhere in a region. If the quantity is a scalar (or vector), the field is said to be scalar (or vector) field. Examples of

scalar fields include temperature distribution in a building, sound intensity in a theater and

electric potential in a region. The gravitational force on a body in space, the velocity of

raindrops in the atmosphere and the velocity of fluid particles in a fluid motion are

examples of vector fields.