Key Terms

Current is the time rate of change of electric charge passing through a predetermined area.

Current density is the measure of the amount of current flowing through a unit area normal to the direction of current flow.

A direct current (DC) is a current of constant magnitude in time.

A sinusoidal current (AC) is that varies sinusoidaly with time.

Frequency is the number of times the direction of current changes (and changes back) per second.
               

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