AC 11


AC 11 : Also See: Current,?Voltage, And?Direct Current. In electricity, alternating current (AC) occurs when charge carriers in a conductor orsemiconductor?periodically reverse their direction of movement. Household utility current in most countries is AC with a?frequency?of 60 hertz (60 complete cycles per second), although in some countries it is 50 Hz. The radio-frequency (RF) current in antennas and transmission lines is another example of AC. An AC?waveform?can be sinusoidal, square, or sawtooth-shaped. Some AC waveforms are irregular or complicated. An example of sine-wave AC is common household utility current (in the ideal case). Square or sawtooth waves are produced by certain types of electronic oscillators, and by a low-end uninterruptible power supply (UPS) when it is operating from its battery. Irregular AC waves are produced by audio amplifiers that deal with analog voice signals and/or music. The?voltage?of an AC power source can be easily changed by means of a power transformer. This allows the voltage to be stepped up (increased) for transmission and distribution. High-voltage transmission is more efficient than low-voltage transmission over long distances, because the loss caused by conductor?resistance?decreases as the voltage increases. The voltage of an AC power source changes from instant to instant in time. The?effective voltage?of an AC utility power source is usually considered to be the DC voltage that would produce the same power dissipation as heat assuming a pure resistance. The effective voltage for a sine wave is not the same as the?peak voltage. To obtain effective voltage from peak voltage, multiply by 0.707. To obtain peak voltage from effective voltage, multiply by 1.414. For example, if an AC power source has an effective voltage of 117 V, typical of a household in the United States, the peak voltage is 165 V. Nikola Tesla, a Serbian-American scientist, electrical engineer, and inventor, developed the alternating-current (AC) electrical system, as well as radio, the Tesla coil transformer, wireless transmission, and fluorescent lighting
No records Found
afaatim.com copyright © April 2016 Dr.K.R.Kamaal. All rights reserved