Home Chapter 3 Current and frequency
Current and frequency

Current (I) is measured in units called amperes (A). The ampere is the rate of flow of electrons during a fixed period of time. One ampere is 6,250,000,000,000,000,000 or 6.25 X 1018 electrons during one second of time.

 

Current (I) is the number of electrons flowing past a point during a fixed period of time.

 

While current refers to the passage of electrons there are also a number of different kinds of current. Direct current (DC) is current that always flows in the same direction. That is, the electrons move in one direction from atom to atom.

DC is the current that runs most of our microcontrollers and other consumer electronic items, but this type of power must come either from a DC source such as a battery or from somewhere else like a converted AC power source. 

Alternating current (AC) is current that varies in magnitude and changes direction periodically. AC is the way power stations and generating stations distribute large quantities of power around the country. It is used because periodically changing the direction and magnitude of the current flow reduces the heat and friction of the electrons.

The current that comes out of your wall socket is AC and runs at 60 Hertz (Hz). Hz designates the frequency of an AC source. The reversing of the direction of AC flow keeps the wires from getting too hot, especially for high power wires conducting tens of thousands of AC volts.

 

The word Hertz comes from the German physicist Heinrich Rudolph Hertz (1857--94), who was the first to artificially produce electromagnetic waves. Hertz is also a unit of frequency, where one Hertz is equal to a periodic interval of one cycle per second.

  
  

This is an image of an oscilloscope used to read and observe the waveforms of AC and DC signals. Directly above the scope is set to read AC and the waveform is showing you how when he sign wave is above the middle of the scope the voltage is going one way and when it is below the middle of the scope it is traveling in the opposite directio

This is another oscilloscope reading a DC voltage. Here the voltage is just a strait line above the center point of the oscilloscope window. You can adjust the value of each square to magnify and look at voltages. (Need image of DC voltage here on oscilloscope 

  

Frequency is the number of cycles over a certain period of time and is generally measured in Hz.

 

DC can have a frequency of varying magnitude, but it will not change direction like AC. Many of you are familiar with the phrase Gigahertz (GHz) from the frequency of your computer processor. A GHz is one billion Hz, or one billion cycles per second. You can have a frequency of 20 Hz or 50 Hz, for instance. Computers use a cycling DC waveform in the GHz range to perform arithmetic computations. The waveform used in computers is a square wave, meaning it will change from 0v to 5v in one cycle. Note that this is different from an AC frequency because only the magnitude of voltages changes, and will never switch from a negative to a positive or vice versa. A typical cycle for AC will progress from a positive voltage, through zero volts, and down to a negative voltage in one cycle.

In the early part of our century, when the captains of industry, Thomas Edison, invented the light bulb, he knew he needed a system to distribute the power necessary to light his bulbs. Edison established local DC generating systems to create the DC distribution network necessary to power his bulbs and motors. Simultaneously, the Westinghouse Electric Company with the inventions of brilliant Nicola Tesla, who was developing AC motors, introduced the competing system of AC. The war of the currents began between Edison’s system of DC and Westinghouse’s AC distribution system. Many dogs, and cats were electrocuted in this war in each side’s attempts to prove that their mode of electrical power distribution was superior.

The contemporary artist Andrew Neumann has created a work that uses the AC signal as a formal element, but instead of displaying an actual sine wave, the artist has captured this form with bent wire. He uses two cameras to capture these waves and transmit them to two LCD screens, which display the characteristic sine waves of the AC signal. Neumann’s work engages issues surrounding the uses of technology, with both the language and the transmission of power. This work is from his Constructures series, which serves to re-contextualize technologically derived iconic forms.

In Neumann’s words the piece is looking at power systems and “questioning its main function as a reflection of the authoritative and corporate powers that it is most clearly aligned and supported by.” [2]

 

:Dual Asynchronous Sine Waves  by Andrew Neumann, 2001, 24" x 32" x 8"

 

In answer to the earlier question, “how do you get electrons to move through materials?” I stated that you need to pile up a bunch of them near the end of the wire and you need a complete circuit.