One cycle includes the variations between two successive points having the same value and varying in the same direction. A radio station transmitter broadcasting at a frequency of 100 MHz generates an AC voltage oscillating at a rate of 100 million cycles every second. The average value is the amount of voltage that would be indicated by a DC voltmeter if it were connected across the load resistor. The reason why an electromechanical alternator outputs sine-wave AC is due to the physics of its operation. 0000036665 00000 n Fundamentals of Alternating Current 5 12.2.4 Average Value The average value of an AC current or voltage is the average of all the instantaneous values during one alternation. This is called frequency. 7.19 The alternating current in a circuit is described by the graph shown in Fig 7.4 . Fig. Publication date 1900 Topics Electric currents, Alternating Publisher New York : Electrical World and Engineer, inc. Collection cdl; americana Digitizing sponsor MSN Contributor University of California Libraries Language English. Don't have an AAC account? Graph of AC voltage over time (the sine wave). During tuning, the value of capacitance is changed. trailer << /Size 86 /Info 53 0 R /Root 55 0 R /Prev 223622 /ID[<17c5df88245a3358193b42a133d36d0b><17c5df88245a3358193b42a133d36d0b>] >> startxref 0 %%EOF 55 0 obj << /Type /Catalog /Pages 51 0 R >> endobj 84 0 obj << /S 326 /Filter /FlateDecode /Length 85 0 R >> stream The handbook includes information on alternating current (AC) and direct current (DC) theory, circuits, motors, and generators; AC power and reactive Alternating-Current Circuits 12.1 AC Sources In Chapter 10 we learned that changing magnetic flux can induce an emf according to Faraday’s law of induction. Theory and calculation of alternating current phenomena by Steinmetz, Charles Proteus, 1865-1923; Berg, Ernst Julius, 1871-1941. NOTES ON ‘ALTERNATING CURRENT’ (Class 12) Page 06 Radio Tuner Tuning is the process of receiving the frequency of a desired radio station. 7.5 7.22 Both alternating current and direct current are measured in amperes. 0000026240 00000 n 0000026218 00000 n Phasors and Alternating Currents v =V cos ωt Ex. If we were to follow the changing voltage produced by a coil in an alternator from any point on the sine wave graph to that point when the wave shape begins to repeat itself, we would have marked exactly one cycle of that wave. source of ac: coil of wire rotating with constant ωin a magnetic field sinusoidal alternating emf. In North America, in fact, where the frequency of the alternating voltage is 60 Hz, the current … They all have the same frequency, but their amplitudes and phases are different. the necessary fundamentals training to ensure a basic understanding of electrical theory, terminology, and application. Other “waveforms” of AC are commonly produced within electronic circuitry. Lecture Notes– El ectrical MachineII [BEE 1401] Part- - I Page | 4 . What graphical shape does an electromechanical alternator follow when produced by AC? 0000003705 00000 n Syllabus of Bachelor of Technology in Electrical Engineering (4th SEMESTER) ELECTRICAL MACHINES-II . Unlike direct waveforms, they cannot be characterised by one magnitude as their amplitude is continuously varying from instant to instant. 15-1: Alternating Current Applications A transformer can only operate with alternating current to step up or step down an ac voltage. Voltage and current are by no means the only physical variables subject to variation over time. 0000001042 00000 n 0000002830 00000 n A view of a piano keyboard helps to put this scale into perspective: Figure below. High-pitch notes such as those produced by a flute or whistle consist of the same type of vibrations in the air, only vibrating at a much faster rate (higher frequency). When graphed over time, the “wave” traced by this voltage of alternating polarity from an alternator takes on a distinct shape, known as a sine wave: Figure below. That is to say, if a wave has a period of 10 seconds, its frequency will be 0.1 Hz, or 1/10 of a cycle per second: An instrument called an oscilloscope, Figure below, is used to display a changing voltage over time on a graphical screen. Figure below is a table showing the actual frequencies for a range of common musical notes. 0000015268 00000 n In particular, if a coil rotates in the presence of a magnetic field, the induced emf varies sinusoidally with time and leads to an alternating current (AC), and provides a source of AC power.