The concepts of voltage and current are not easy to explain. Both properties are invisible to the human eye, and work in ways that are counter-intuitive. The only reasonable means with which to explain the properties of electric voltage and current would be to relate it to more visible, everyday terms, such as the flow of water in pipes. Most people have used come type of faucet or plumbing fixture in their lifetimes, and therefore can visualize water flowing from some form of piping or valve. Another general means of conceptualize the flow of water would be a river or stream. This flow of water is often referred to as the stream (or pipe’s) current, which analogous to the current flowing in an electric wire. Just as in an electric wire, the bigger the pipe, the more water that can flow through it, so the more current the pipe can allow. The comparison holds up so well that even the amount of resistance from the size of the pipe can be related to the resistivity of the electric wire. Electric current is measured in Amps, or Amperes everywhere across the globe.
Voltage is somewhat more difficult to conceptualize. Electric Voltage in the past and still throughout modern industries is referred to as “electric potential” or “electro-motive force.” Much like the force of gravity pulls water down pipes or mountainsides, this “potential” of electricity causes electric current to flow through wires from higher to lower voltage. Therefore, voltage can be somewhat conceptualized as analogous to the vertical drop with which water traverses in a waterfall or through plumbing. The higher the voltage, the higher the waterfall (or water tower). Since the pressure of the water in plumbing is directly proportional to the height of the water tower, it is also correct to conceptualize electric voltage to being analogous to the pressure of the water within the pipes as well.
With electrical applications, power is simply the voltage of the wire multiplied by the current running through it. In the analogous plumbing terms, it’s easier to think of it as the amount of water falling by the distance it fell. Kind of like the area of a waterfall…a short but wide waterfall might have the same power output as a narrow but tall waterfall. Naturally, a waterfall that was both tall and wide would have higher power output than the previous two mentioned. The exact same rules apply for the voltage and current of an electric circuit.
Resistance is somewhat tricky to describe in terms of a water-analogy. The resistivity of the pipes themselves matches well with electrical wiring; so in essence, the electrical component of a resistor can be seen analogous to a section of smaller pipe inserted into an otherwise thicker pipe of water. This smaller section causes back-pressure on the water-line, causing the overall current in the pipe to drop by a certain amount. The higher the resistance, the smaller the pipe. This is exactly the same as how electrical current responds to a resistor in a wire. With electrical wiring, the amount of current passing through a wire is dependent on the voltage of the electricity applied to the wire as well as the resistance of the load or resistor placed in the circuit. This relationship is known to the Electrical Engineering community as Ohm’s Law, which states that: the current between two points on an electrical circuit is proportional to the voltage difference across those two points. An image of this relationship is shown below.
The last major concept to cover in terms of electricity is the diode, or one-way valve for electricity. Without focusing too much on the details of a diode’s construction, it’s a component that only allows current to flow in a single direction through it. Essentially, the mechanism for which this accomplished is very similar in concept to a waterfall. An intrinsic potential voltage is created within the component’s material itself, creating somewhat of a “ledge” that electric charge can flow across from higher-to-lower potential. However, just like in a waterfall, the charge is not able to flow from a lower ledge to a higher one. While the mechanism for which this accomplished is done through semiconductors, the fundamental concepts still hold true throughout the analogy between water and electric charge.
http://sargosis.com/articles/science/intro-guide/basic-electric-concepts/
