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Electric Field

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Electric Fields

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Electric Field


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Students observe the behavior of electric field lines in the electric fields of both positively and negatively charged particles.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • After completing this Activity Object, learners will be able to:
  • Explain the properties of an electric field.
  • Define the characteristics of electric field lines.
  • Explain that the electric field lines of the positive charges head away from the charge.
  • Explain that the electric field lines of the negative charges head toward the center of the charge.
  • Explain how the magnitude of an electric field varies depending on the change in distance between the charge’s initial and final locations.

Everything You'll Have Covered

Coulomb's Law states that an electric force results from and acts on charged particles, and that it defines the resulting force in terms of the charges and the distance between them The force exerted by a source charge Q on another (test) charge q, therefore, varies with distance and with the magnitude and sign of the charges. From Coulomb's Law, we can determine an electric field for Q. A field is a space in which, for each and every possible point in that space, a quantity is defined. The electric field is defined as the electric force that would be experienced by a test charge of +1 at a given distance away from the source Q. Because force is a vector quantify, the electric field is a vector field.

The electric field on an isolated point charge spreads radially outward uniformly in all directions. It is represented by electric field lines pointing toward negative charges and away from positive charges. (Electric field lines are merely representations; in reality, an infinite number of field lines would emanate from a point charge.) In this way, the electric field is analogous to the gravitational field from a spherical mass. But unlike gravity, which attracts all masses, an electric field exerts opposite effects depending on the test charge. On a positive charge such as a proton, the electric field exerts a force in the direction of the field. A negative charge, such as an electron, experiences a force in the opposite direction.

In an electric field, the force acting on a particle of unit charge decreases according to the inverse square of the distance from the source. The force also increases as the charge generating the field increases. The formula for electric field is given by where k is Coulomb's constant, q is the source charge, and r is the distance from the source charge. Therefore, E is the force per unit charge of the source (E = F/Q) and is measured in newtons per coulomb (N/C) or volts per meter (V/M).

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Students should be able to define the properties of force as a vector quantity and explain the interaction between electrical charges.
Course Physics
Type of Tutorial Concept Development
Key Vocabulary charged particles, coulombs, Coulomb’s constant