My second post in the electrical misconceptions series relates to the use of terms in this topic.
The topic of electricity contains several abstract terms; voltage, current, resistance, energy, power etc. and students have understandings of some of these terms (current and resistance) from other areas of their lives. The other terms are more abstract because students often do not have a clear understanding, or framework or visual representation of what they mean. Of course, the terms that they have some kind of context for (current and resistance) may actually be leading to a further misconception because the meaning may vary in alternative contexts.
Students often have difficulty with electrical circuit problems. In my experience, most of these difficulties are due to misconceptions.
Here is one of the most commonly held misconception;
Electricity exits the battery at the positive side, travels around the circuit and ends up at the negative side.
There are a few other related misconceptions that come out of this statement;
- The moving charge, called electricity, travels at the speed of light
- The wires are like empty pipes that the electricity travels through
- Multiple bulbs in series are of ever decreasing brightness, with the bulb nearest the positive terminal of the battery the brightest, followed by the bulb next to it and so on.
- Resistors need to be on the positive side in order to do their job of limiting the electricity (or current) after it.
I’m sure there are more, but these are all linked to a single misconception; that the battery supplies the current, or charge, or electricity, to the circuit.
Alternating current and direct current are the two main forms of charges powering our electric and electronic world. If you have heard the names AC and DC for the first time, then this Buzzle article will be very helpful in introducing the basic concepts about these power sources.
What is AC?
An alternating current can be defined as a flow of electric charge that changes its direction at regular intervals. The period/regular intervals at which an AC changes its direction is termed as its frequency (Hz). This current can be represented on a graph as a sinusoidal wave. Marine vehicles, spacecrafts, and military equipment sometimes use AC with a frequency of 400 Hz. However, for most of the time, including domestic use, the frequency of AC is fixed at 50 or 60 Hz. The households in the U.S. are supplied with 60 Hz AC, whereas the frequency of alternating current for domestic purposes is 50 Hz in European countries.
What is DC?
Direct current is a current (flow of electric charge or electrons) that flows only in one direction. If represented on a graph, DC can be plotted as a straight line as it does not change direction. Subsequently, there is no frequency associated with a DC. If you are a student, the frequency of DC is normally asked as trivia. The fact is DC or direct current has zero frequency.