By Ohms law, I is simply the source voltage divided by the total circuit resistance.Circuit Theorems and Conversions DK 8 Electric Circuit 2 Chapter 8 Circuit Theorems and Conversions.
Electric Circuit 3 OUTLINE Electric Circuit 4 The DC voltage source. Maximum Power Transfer Theorem. Electric Circuit 73 Maximum Power Transfer Theorem Electric Circuit 74 Maximum Power Transfer Theorem. Objective of Lecture Explain the maximum power transfer theorem. Chapter 4.8 Fundamentals of Electric Circuits. Maximum power transfer theorem is used frequently to insure that the greatest power can be transferred from a power source to a load. In electrical engineering, the maximum power transfer theorem states that, to obtain maximum external power from a source with a finite internal resistance, the resistance of the load must equal the resistance of the source as viewed from its output terminals. The theorem results in maximum power transfer across the circuit, and not maximum efficiency. If the resistance of the load is made larger than the resistance of the source, then efficiency is higher, since a higher percentage of the source power is transferred to the load, but the magnitude of the load power is lower since the total circuit resistance goes up. If the load resistance is smaller than the source resistance, then most of the power ends up being dissipated in the source, and although the total power dissipated is higher, due to a lower total resistance, it turns out that the amount dissipated in the load is reduced. The theorem states how to choose (so as to maximize power transfer) the load resistance, once the source resistance is given. It is a common misconception to apply the theorem in the opposite scenario. It does not say how to choose the source resistance for a given load resistance. In fact, the source resistance that maximizes power transfer is always zero, regardless of the value of the load resistance. The theorem can be extended to alternating current circuits that include reactance, and states that maximum power transfer occurs when the load impedance is equal to the complex conjugate of the source impedance. ![]() In 1880 this assumption was shown to be false by either Edison or his colleague Francis Robbins Upton, who realized that maximum efficiency was not the same as maximum power transfer. To achieve maximum efficiency, the resistance of the source (whether a battery or a dynamo) could be (or should be) made as close to zero as possible. Using this new understanding, they obtained an efficiency of about 90, and proved that the electric motor was a practical alternative to the heat engine. The condition of maximum power transfer does not result in maximum efficiency. If we define the efficiency as the ratio of power dissipated by the load, R L, to power developed by the source, V S, then it is straightforward to calculate from the above circuit diagram that. ![]() Efficiency also approaches 100 if the source resistance approaches zero, and 0 if the load resistance approaches zero. In the latter case, all the power is consumed inside the source (unless the source also has no resistance), so the power dissipated in a short circuit is zero. In radio frequency transmission lines, and other electronics, there is often a requirement to match the source impedance (at the transmitter) to the load impedance (such as an antenna) to avoid reflections in the transmission line that could overload or damage the transmitter. In the diagram opposite, power is being transferred from the source, with voltage V and fixed source resistance R S, to a load with resistance R L, resulting in a current I.
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