Associated with a charge or charge density, permeating the space surrounding the charge, the electric field at a location represents the capability the charge or charge density has to exert force on another charge were one placed there. The electric field strength tells you how many Newtons of force per Coulomb of charge would exert upon the charge placed in the field.

We employ the concept of the test charge to imagine learning about about the force producing character of the field. Placing the charge in various places, we would learn the strength and direction of the field in those places, how many Newtons of force per Coulomb of charge it represents.

Analogously, we could employ the test charge to learn about the energy storing character of the field between two positions. In this case, we would be learning about the electric potential, or voltage. We could push or pull our test charge around and measure how much work is required to move from point A to point B in the field. Voltage represents hypothetical work, joules of work per coulomb of charge, required to move a test charge from point A to point B within the field under study.

So, in summary, while the electric field represents the ability of a charge (or charge distribution) to exert force on hypothetical charges; the voltage represents the ability of a field to perform work on a hypothetical charge.
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