Sara Bader, Cathy Becker, Phil Lee, Alyssa Stern

Mr. Kuehl

Pre-Calc

23 December 2006

Electrical Circuits and Switches

            Every day in homes and businesses around the world, something astounding occurs. Someone reaches for a small piece of plastic, moves it a short distance, and the room is suddenly and inexplicably flooded with light. Perhaps this does not sound extremely amazing since it is such a commonplace occurrence in our society, but people rarely stop and actually think about how the flick of a switch can bring light to a previously dark room. Without the use of electrical circuits, artificial lighting would be impossible. The development of a variety of electrical switches has made life easier for people around the world.

Circuits came into common use with the introduction of Thomas Edison’s incandescent lamp. Edison knew that in order for his lamps to work, electricity had to travel in a circular path to keep the flow of electrons moving. He used direct current, in which the flow of electrons moves constantly in one direction. The disadvantage to Edison’s direct current method was the fact that high voltage could not be achieved. This meant that the electricity generated at a power plant could only travel about two miles without losing too much power to be practical. Nikola Tesla was working in Edison’s lab when he realized that the direct current system did not make full use of the potential electricity had. He thought that since energy tends to travel in cycles, harnessing electricity should mimic nature. To do this, Tesla developed the alternating current system in which the current changes direction fifty or sixty times per second. This new system enabled the voltage to be increased to higher level, which allowed the electricity to travel long distances without losing much power. Edison had invested in his direct current system and was unwilling to see it be overtaken by Tesla’s alternating current. The newer technology was superior, however, and therefore eventually became the standard for electricity as Edison’s direct current passed into disuse. Alternating current is used today to carry electric current in wires over long distances and in lighting and electrical machinery. In the case of other devices, such as computers, stereos, or televisions, the alternating current must first be converted into direct current before it can be useful.

Electricity experienced a revolution in the late 1950s when the need for a large number of circuits to perform linked operations became prevalent. To solve this problem, Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Camera developed the integrated circuit. In this new method, several transistors, resistors, capacitors, or diodes were made at one time. Multiple pieces could be put on the same piece of semiconductor. For his work in creating integrated circuits, Jack Kilby was awarded the Nobel Prize in Physics in 2000. Since Kilby and Noyce’s breakthrough, the size of transistors has been decreasing at an astounding rate. Moore’s Law (named for Gordon Moore, a pioneer of the early integrated circuits and founder of Intel Corporation) states that the number of transistors per unit area has doubled every 1 ½ years from the 1960s until the present.

There are several parts necessary for any electrical circuit. When the components of a circuit form an unbroken path, the circuit is referred to as closed and can conduct electricity. An electric cell provides the power for the circuit. The load is often a lamp or another resistor, and is the purpose for the circuit. These two components are connected by wires that complete the circuit. If a circuit is “closed”, it can conduct electricity, and the lamp will light up. If, however, the circuit is “open” or “broken,” the lamp will not be able to light since the flow of electricity has been interrupted. Circuits are changed between closed and open with the use of switches, fuses, or circuit breakers.

There are two basic types of circuits: series and parallel. In a series circuit, the components are connected end to end to form a single path of electrons. If there is more than one bulb in the circuit, the lights get progressively dimmer the farther they are from the power source. If one light is missing from the circuit, the entire circuit does not work. An example of this is old Christmas lights. If one light burned out, you would have to spend hours figuring out which light is missing since they would all turn off. Parallel circuits have at least two independent, closed-circuit paths for electricity to travel before returning to the source. Since the paths are independent, multiple bulbs in the circuit will all be of the same brightness. Even if one light is removed from a parallel circuit, the rest of the lights will still remain lit.

            In addition to there being different types of circuits, there are also different types of switches that are useful in different situations. Switches are defined in terms of poles and throw. Poles are the number of wires the switch controls, and a throw is the number of positions the switch can be in that makes a connection. A single-pole single-throw switch is a simple on-off switch. Either the switch is open or closed. This type of switch is commonly used for turning on lights since the light need to be either on or off.

But what if you need to turn of a single light from more that one location, such as at the top and bottom of a stairway or on both ends of a hallway. A type of switch useful in a situation like this is a single-pole double-throw. When in one position, the switch will complete one circuit, and if the switch is changed to a second position, it completes a second circuit. There may also be a center off position in which no circuits are completed. This type of switch can be used when you want to switch between two on operations such as transmitting/receiving on a two-way radio or high/low beam headlights. The most common use for this switch is areas where you need to turn one light on from two different places, such as at the top and bottom of a flight of stairs. When both switches are up, the circuit is complete, and the light is on. When you throw one switch down, the circuit is broken, and the light turns off. When you throw the other switch, both switches are down so the circuit is complete again.

A double-pole double-throw switch is highly complicated. It can be used for lights that need to be controlled for three or more locations. The input is wired to the top two terminals. These are then connected in a “criss-cross” fashion to the bottom two terminals. The switch is attached to the middle terminals and move in unison up or down (see figure at right). The middle terminals also serve as the output. If the switches are up, the current never reaches the output. However, if they are down, the current travels through the input (top) terminals, across the wires connecting top to bottom, and up to the middle terminals and the output.  The double-pole double-throw switch is placed between two single-pole double-throw switches. This produces the same effect as single-pole double-throw switches but now can control the single light from more locations. If all the switches are flipped up, the circuit will be open, so the light will be off. Flip one of the single-pole double-throw switches down, and the electric current can run through the closed circuit. Flipping the double-pole double-throw switch down will break the circuit again. This type of switch is useful in rooms with tree or more exits.
By now you should be able to see the complexity and importance of electrical circuits and switches in our everyday lives. Without the diverse types of circuits and switches, life would be an endless struggle of trying to find the one burnt-out bulb in a sea of functional ones and running up and down the stairs to turn the lights on and off. So the next time you walk into a dark room, take a moment to pause and think, “What is going on here that I take for granted every day?” Remember each time you flip a switch the long journey the electricity travels before reaching its final destination. If we take time to simply reflect on how the circuits and switches that surround us work, we may truly be amazed with the ingenuity, time, and effort it took to develop such technology. The next time you flip a switch to fill a room with light, the dark corners of your mind may also be illuminated with the knowledge of how circuits and switches work.

Sources

<http://nobelprize.org/educational_games/physics/transistor/history/>

<http://www.aegee-beograd.org.yu/aegee-bgd/eng/tesla.php>

<http://en.wikipedia.org/wiki/Series_and_parallel_circuits>

<http://columbia.thefreedictionary.com/electric+circuit>

<http://www.1728.com/project2.htm>

 

<http://www.iqsdirectory.com/electric-switches/>

 

<http://www.reprise.com/host/electricity/schematic1_notes.asp>

 

<http://64.233.161.104/search?q=cache:aRimI9UG45kJ:www.gaugemaster.co.uk/instructions/switches_explained.pdf+how+circuits+work,+single-pole+double-throw,+double-pole+double-throw&hl=en&gl=us&ct=clnk&cd=12>

 

<http://www.glenbrook.k12.il.us/gbssci/phys/Class/circuits/u9l4b.html>

 

<http://en.wikipedia.org/wiki/Switch>

 
Circuits Main Page
Circuits Research Page
Circuits Construction Directions
Circuits Study Guide