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Electricity - Voltage and Current  Voltage: Voltage , also called electromotive force , is a quantitative expression of the potential  difference in charge between two points in an electrical field. Voltage can be direct or alternating. A direct voltage maintains the same polarity at all times. In a n alternating voltage , the polarity reverses direction periodically.         ·        Voltage is a measure of the energy carried by the charge.         ·        Voltage is supplied by the battery (or power supply)         ·        Voltage is measured in volts, V. Symbol is V         ·        Voltage is measured with a voltmeter, connected in parallel. Current: The quantity of charge carries that pass a fixed point per unit of time (the rate electron flow). ·        Current is the rate of flow of charge. ·        Current is measured in amps (amperes) A. Symbol  is I ·        Current is measured with an ammeter, connected in series.

Are Voltage and Current Related?  Voltage and current are not the same thing, although they are closely related. In simple terms, Voltage causes Current. Given a Voltage and a path for the electrons, current will flow. Given the path, but no Voltage, or Voltage without the path, there will be no current.

A Simple Circuit      This picture illustrates a single cell pocket flashlight. The 1.5 Volt cell is pushing the electrons through the bulb and the wire. Without this push, the electrons would be happy to remain stationary. In this case, chemical action within the battery causes the push. When the battery gets old, its chemical reaction slows down and its internal push gets weaker and weaker. (That's why the bulb gets dim.)

Who Does the Work?  Current, not Voltage, does the work in electrical circuits. The flow of water through a turbine is what makes the turbine spin. The flow of current through an electrical circuit is what lights the bulb, heats the stove, runs the motor, etc. Routing and controlling the flow of current is the goal of every electrical circuit.

         **Voltage is the Cause, Current is the Effect**

Electricity - Resistance

Resistance  Resistance is the friction in an electrical circuit that controls the flow of current.  As previously mentioned, voltage causes current. When a voltage is present and there is a path (circuit) for electron flow, then there will be a current.