Electric Fields: Definition & Examples

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  • 0:00 Definition
  • 0:59 Static Electric Fields
  • 3:49 Dynamic Electric Fields
  • 5:20 Lesson Summary
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Lesson Transcript
Instructor: Thomas Zesiger

Thomas has taught electronics and communications engineering, math, and physics and has a master's degree in electrical engineering.

Learn what an electric field is, the types of electric fields, and the concept of electric field strength. Briefly investigate specific examples of the types of electric fields.


An electric field is the force that fills the space around every electric charge or group of charges. Electric fields are caused by electrical forces. Electrical forces are similar to gravitational forces in that they act between things that are not in contact with each other. Electric fields are also analogous to magnetic fields resulting from forces acting upon magnetic substances or magnet poles. Electromagnetic waves have both an electric field and a magnetic field that are coupled to each other. Mathematically, the magnitude (or the strength) of an electric field at any point is defined by the force experienced by the charge at that point divided by the charge. This concept is written mathematically as E = F / q. Electric field strength is measured in units of newtons/coulomb. Electric fields are either static or dynamic.

Static Electric Fields

Static electric fields, or electrostatic fields, are produced by stationary charges and are uncoupled to magnetic fields. You may have experienced this same phenomenon when laundry items cling to one another during removal from the dryer. Lightning is also caused by the very strong static electric field between a cloud and the earth.

The electric field has a clear direction and specific intensity at every point within the field. This is due to the fact that the force exerted on any particular charge varies in magnitude and direction from point to point within the field. Electric fields are represented by lines in the same way as magnetic fields.

This image shows the electric fields around isolated positive and negative charges, two unlike charges (one positive and one negative) and two like charges (both positive). The arrows on the lines show the direction in which the electrical forces act. The separation between the lines indicates the electric field strength. As can be expected, the farther away we get from the charges, the weaker the strength of the electric field. You can also see, just like with magnetic fields, unlike electric charges attract, and like charges repel each other. Electric field lines around a positively-charged particle point radially outward, and the lines around a negatively-charged particle point radially inward.

The force with which two electric charges attract or repel each other is directly proportional to the square of the distance between the two charges. Stated another way, if the distance between the two charges is cut in half, the force between them is quadrupled. If the distance between the two charges is doubled, the force between them is one-fourth of the original force.

An example of an electrostatic field is one that is produced in a parallel-plate capacitor. A parallel-plate capacitor consists of two parallel plates with the same surface area separated by a certain distance. The volume between the plates is filled with a dielectric material. A dielectric material is also called an insulator. In a perfect dielectric, no current flows through the material. Examples of dielectrics include glass, paraffin, mica, and quartz.

A direct current (DC) voltage source is connected to the two conducting plates. Charge of equal and opposite polarity is transferred to the surfaces of the conductors. Because of the applied voltage difference, positive charge accumulates uniformly on the plate connected to the positive voltage terminal, and negative charge accumulates uniformly on the plate connected to the negative voltage terminal. In the dielectric medium between the plates, the charges induce a uniform electric field in the direction from positive to negative charges.

Dynamic Electric Fields

Dynamic fields, or time-varying fields, are induced by time-varying sources. Time-varying fields are used to produce electromagnetic waves, which are used in such things as radio and television broadcast equipment, radar, X-rays and ultrasound machines, microwave ovens, cellular and cordless phone systems, and wireless routers.

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