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Introduction |
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Do we use dry cells for operating electrical appliance? It is not impossible to tap continuous supply of energy from electrochemical cells. Electrical circuits in homes, factories and offices receive such energy form local power companies. In most countries the energy is supplied via oscillating e.m.fs and currents. These oscillating currents are called as alternating currents, shortly as a.c. |
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AC Circuit Containing Resistance only |
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Let an AC source of EMF E be connected to a pure resistance R. The instantaneous EMF from the source. |
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Phasors |
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Phasors rotate clockwise about the origin with angular speed equal to the angular frequency of current and voltage. |
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AC Circuit Containing Pure Inductance only |
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Let an AC source be connected across a pure inductive element. If the alternating current I = Io sin wt flows through it. |
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AC Circuit with Pure Capacitance only |
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Let an AC source be connected across pure inductive element. |
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AC Circuit Containing Resistance, Inductance and Capacitance Circuit (LCR in series) |
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When an AC source is connected in a circuit with a resistance and a reactance together, the current varies initially in a complex way. After sufficient time, a sinusoidally varying current persists in the circuit. This steady state current has a frequency equal to that of the source and may have a phase difference with the source voltage. |
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Series Resonant LCR Circuit |
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The circuit behaves like a pure resistive one, the current and voltage are in phase. This fact helps in tuning our TV and radio sets. |
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Average Power Associated with LCR Circuit in Series |
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In an electrical circuit, energy is supplied by the source of EMF, stored by the capacitive and inductive elements and dissipated in resistive elements. |
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L.C. Oscillation |
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Capacitors and inductors are capable of storing energy in the electric field and magnetic field respectively. |
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AC Generator or Dynamo |
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An 'AC generator' or 'dynamo' is a machine which produces AC from mechanical energy. Actually, it is an alternator which converts one form of energy into another. |
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Transformer |
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An electrical device is used to change the AC voltage. A transformer which increases the AC voltage is called a 'step up transformer' and a transformer which decreases the AC voltage is called a 'step down transformer'. |
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Summary |
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An alternating current is that which changes continuously in magnitude and periodically in direction. It can be represented by a sine curve or a cosine curve. |
