Electricity is one of the foundations of our world: our modern way of life would grind to a halt were there no electricity to run our myriad of gizmos and gadgets. As such, an entire field of engineering dedicated to keeping the juice flowing and finding ways of using that power to do all sorts of interesting things has developed. Most of us, however, are content just to know that if you plug your TV into the wall outlet and press the power button, you can watch your favorite diversions to your heart's content. This article will sort out the mysteries of volts, amps, watts, and other concepts in electricity.
How important is electricity? Without it, the monitor with which you are viewing this article right now would not work, nor would the CPU which decodes this web page and tells your monitor what to display. Given the importance of computing and the internet/email in the worlds of business, finance, science, and daily life, this alone is a rather important reason to ensure that the juice keeps flowing.
Besides its role in the recent computer and internet revolution, electricity plays a vital role in modern industry, whether to power industrial robots or to harness the raw power of huge electrical currents to melt iron in steel foundries.
So, just what is electricity? The basic definition is quite simple to understand: electricity is a flow of electric charge. Charge is a fundamental quantity in physics (i.e., it cannot be described in terms of yet more basic concepts) which all of the fundamental subatomic particles which make up our world carry (neutrons are not fundamental particles but are made from charged particles whose charges happen to cancel).
The amp, short for ampere (named after eighteenth century French physicist Andre-Marie Ampere) is the basic unit of electric current. Electric current is quite analogous to a flow of water: the amount of "stuff" that goes past a point in a certain time is the current at that point. In the case of water, or any other fluid, engineers use a term called volume flow rate, which is the volume of said fluid that passes through a certain cross-sectional area per unit of time (e.g., X cubic meters per second). The definition of electric current is similar, except that the "stuff" being measured is the amount of electric charge passing through an area such as a point on a wire.
Voltage, on the other hand, is a somewhat trickier concept to put into familiar terms. What we call "voltage" is actually an informal reference to electric potential difference (no wonder we find it easier to say "voltage" instead!). The closest analogy to a flow of water is to the pressure difference in a pipe; absent any greater momentum in the opposite direction, water will flow from the area of greatest pressure to the area of least pressure. While pressure creates a "potential" in the case of water, it is a difference in charge which creates this potential in the case of electricity: a current is simply nature's way of trying to even out an imbalance of charge by sending negative charges to an area where there is a relative deficiency of negative charge (i.e. a more positively charged region), or vice versa.
A "volt," then, is a unit of electric potential difference. The simplest way to think of the number of volts is as the amount of desire electrons in the current have to get across the distance separating the differently charged regions. That is, the "voltage," or potential difference, across a gap of a given distance varies with the amount of the difference in charge from one side of the gap to the other. If one side of the gap has five units of positive charge and the other side five units of negative charge, the voltage will be five times greater across the gap than if there were one unit of positive or negative charge on each respective side.
The watt (named after Scottish inventor and engineer James Watt), finally, is a unit of power, just like the horsepower is a unit of power. Since power is the same quantity in the eyes of physics whether it comes in the form of electrical power or mechanical power or any other form of power, nothing about the watt is particular to electricity.
Now what is "power," you ask? A physicist defines power as the amount of work done (or the amount of energy used) in a certain amount of time. Imagine two cars, a typical family sedan and a high-powered racing car, each given the same amount of the same type of fuel. The amount of fuel in the tank is the energy reserve a car has available, and since each car has the same amount of the same fuel, each can theoretically travel exactly the same distance before running out of fuel and rolling to a stop (assuming equal mass and the same conditions for each car). If both cars are cranked to their maximum output, however, the regular sedan may take twice as long as the race car before it finally rolls to a halt beside its sexier counterpart, in which case we would say it has half the power of the race car (but equal energy).
In electricity, it turns out that power is the product of current and voltage. Thus, multiplying the potential difference (in volts) in a wire by the current (in amps) gives you the power coursing though the wire, in watts. Since voltage and current can be interchanged to give the same power output, transformers are used to achieve the optimal trade-off between current and voltage in power transmission lines. In this case, the lowest possible current is optimal since higher currents demand thicker wires and create more heat, so the voltage is stepped up to very high levels in power lines and then stepped down to regular line voltage at the power station for distribution to local users.
While it may seem simple to plug in a TV and "zone out in front of the 'tube," there is reason to understand the basics of electricity. The world is not as simple as it may seem, because each appliance or cell phone or laptop computer is designed to run on a different line voltage, at a different current, for a different power rating. Feeding a part less power than it needs would be relatively harmless, but doing the opposite can destroy that device you shelled out hard earned money for! With the information presented here in mind, you may now know what a user guide means when it specifies power requirements for a part, and hopefully this will make your life easier.
