In Europe, where the power system frequency is 50 Hz, the AC voltage only completes 50 cycles every second. source of ac: coil of wire rotating with constant ωin a magnetic field sinusoidal alternating emf. Alternating Current Theory - J R Lucas An alternating waveform is a periodic waveform which alternate between positive and negative values. They are actually DC values. 0000001042 00000 n Following this rule, the next highest “A” note (one octave above 440 Hz) will be 880 Hz, the next lowest “A” (one octave below 220 Hz) will be 110 Hz. qs>5M�ٷ?�# Syllabus of Bachelor of Technology in Electrical Engineering (4th SEMESTER) ELECTRICAL MACHINES-II . �� pQ���(Z)h@��PX h0�C��o@��, �\� 9E� ��������,Za+E��R9�{f���/Q����ۀ� �emu�/P��ŋ @)j0-@)��� ��=� ����}~6�uԚ�g����� O�����c`��b$L4��t&c�9h�}�t9�?\�������� Onu 0000001961 00000 n The same 2:1 ratio holds true for the first A sharp (233.08 Hz) and the next A sharp (466.16 Hz), and for all note pairs found in the table. As you study this and the following modules on AC (Alternating Current) theory, notice that the circuits described use two main components, inductors and capacitors, which in many ways seem to have opposite and complimentary effects. 0000003815 00000 n A similar change occurred when the unit of “Celsius” replaced that of “Centigrade” for metric temperature measurement. The degree marks on the horizontal axis of the graph represent the domain of the trigonometric sine function, and also the angular position of our simple two-pole alternator shaft as it rotates: Figure below. 0000026218 00000 n 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 0000015290 00000 n When an alternator produces AC voltage, the voltage switches polarity over time, ... A more popular measure for describing the alternating rate of an AC voltage or current wave than period is the rate of that back-and-forth oscillation. The name Celsius, on the other hand, gives no hint as to the unit’s origin or meaning. 0000036643 00000 n NOTES ON ‘ALTERNATING CURRENT’ (Class 12) Page 06 Radio Tuner Tuning is the process of receiving the frequency of a desired radio station. Alternator voltage as function of shaft position (time). Much more common to our everyday experience is sound, which is nothing more than the alternating compression and decompression (pressure waves) of air molecules, interpreted by our ears as a physical sensation. Chapter AC – Alternating Current Circuits Page 1 At first glance, this graph just shows a jumble of sine waves. Even in circuits that are supposed to manifest “pure” sine, square, triangle, or sawtooth voltage/current waveforms, the real-life result is often a distorted version of the intended waveshape. Lecture Notes– El ectrical MachineII [BEE 1401] Part- - I Page | 4 . A view of a piano keyboard helps to put this scale into perspective: Figure below. They all have the same frequency, but their amplitudes and phases are different. This similarity in sound is musically recognized, the shortest span on a musical scale separating such note pairs being called an octave. alternating current – in fact, both the current and the voltage oscillate sinusoidally. Voltage and current are by no means the only physical variables subject to variation over time. Thus various forms of magnitudes are defined for such waveforms. %PDF-1.2 %���� = 120 120 f 120 x 50 20 poles 2.4 Here, i = (cot + O) Here given. The name Centigrade was based on a 100-count (“Centi-”) scale (“-grade”) representing the melting and boiling points of H2O, respectively. 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. H�T�I��@����>�h�.�MB�2$Y�܍�F�Ƌ�9��S�)�ʯ����J���Է�K~LCu��kھ��m�OUt�xm{��m5?��UW�.����m�ݩo��-���x���{9?�����_]�}����W��+�����>������sW�f�_��[�E]~�� �:�Ʋ�S�_�����]*��}���"[ڑKc߶�$-�������H�h;V02ęܱD�w++����F�9~����5�iK�#� It consists of an inductor and a variable capacitor. The familiar musical mnemonic (doe-ray-mee-fah-so-lah-tee)—yes, the same pattern immortalized in the whimsical Rodgers and Hammerstein song sung in The Sound of Music—covers one octave from C to C. While electromechanical alternators and many other physical phenomena naturally produce sine waves, this is not the only kind of alternating wave in existence. i = I cos ωt v, i = instantaneous potential difference / current. 7.19 The alternating current in a circuit is described by the graph shown in Fig 7.4 . Astute observers will notice that all notes on the table bearing the same letter designation are related by a frequency ratio of 2:1. The handbook includes information on alternating current (AC) and direct current (DC) theory, circuits, motors, and generators; AC power and reactive Audibly, two notes whose frequencies are exactly double each other sound remarkably similar. 0000002170 00000 n The average value is the amount of voltage that would be indicated by a DC voltmeter if it were connected across the load resistor. One cycle includes the variations between two successive points having the same value and varying in the same direction. 0000002830 00000 n By measuring the period of the wave on the horizontal axis of the oscilloscope screen and reciprocating that time value (in seconds), you can determine the frequency in Hertz. Low-pitch notes such as those produced by a tuba or bassoon consist of air molecule vibrations that are relatively slow (low frequency). If we were to graph the trigonometric function of “sine” over a horizontal range of 0 to 360 degrees, we would find the exact same pattern as in the Table below. Topics Page No. PN 10 x 360 120 = 120 -30 Hz (b) Here, 120 120f For f = 25 Hz N = 500 rpm f = 60 N = 1200 rpm 2.2 Here. 0000002276 00000 n :(����[#Ke��HV&_z�����ы�d���p�I��d�y�Y&Gws �{8j��.\Z�GKSv�����%8 Published under the terms and conditions of the. 0000001850 00000 n DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other. You may be familiar with the appearance of an ECG or EKG (electrocardiograph) machine, used by physicians to graph the oscillations of a patient’s heart over time. Unlike direct waveforms, they cannot be characterised by one magnitude as their amplitude is continuously varying from instant to instant. A more popular measure for describing the alternating rate of an AC voltage or current wave than period is the rate of that back-and-forth oscillation. Create one now. 0000019720 00000 n the necessary fundamentals training to ensure a basic understanding of electrical theory, terminology, and application. 0000001660 00000 n 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. H��W˲��-�I��Y�af�L����RJ�$�\W�} �y�����t�^$�X�̣����_��R���_�^���;�>tm�R��4*-���T�h�:֋��W�ŋo.��E'*Ə'yLg��l���-b��8�cZZ/�4�s�zZ��zj�Z�id�mXFeP�:�<=b�폡�Q(��Ѐ�@�ur�>���x���݄� 0000041204 00000 n The handbook includes information on alternating current (AC) and direct current (DC) theory, circuits, motors, and generators; AC power and reactive 0000003010 00000 n In the United States of America, the standard power-line frequency is 60 Hz, meaning that the AC voltage oscillates at a rate of 60 complete back-and-forth cycles every second. What this means for the light bulb filament is that the current reverses direction at regular intervals. 54 0 obj << /Linearized 1 /O 56 /H [ 1042 411 ] /L 224830 /E 48648 /N 15 /T 223632 >> endobj xref 54 32 0000000016 00000 n Thus various forms of But how is the ampere defined for an alternating