Electric Charge

Coulomb's Law

Electric Field

Continuous Charge Distributions

Mechanical Universe (MU): Introduction

MU:  Static Electricity

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Electric Fields

The electric field at a point in space is defined as the force per unit charge acting on a small positive test charge q₀ placed at that position:

The SI units of electric field are N/C.

For a point charge, Coulomb’s law may be used to find the magnitude of electric field:

It is important to remember that electric field, like force is a vector. The electric force on the small positive test charge q₀ used to define the electric field vector. If there are multiple charges, the the test charge measures the vector sum of electric fields due to each charge.

Examples

A point charge identical to the one in the center of the applet window is located somewhere outside of the window area. Drag the green test charge and determine the location of the unseen charge. Click to check your answer.

In the applet below, click Like charges or Unlike charges to see two point charges, along with a test charge. Move the test charge around to see the relationship between electric field lines and electric field vectors. Be sure to wait for the applet to finish calculating before moving the test charge.

Question: what is the relationship between electric field vectors, and electric field lines?