Electrical Engineering ⇒ Topic : Effect of source resistance on current and power in a series circuit
TABLE Effect of source resistance on current and power in a series circuit
The above table clearly shows that the effect of the source resistance becomes small when the load resistance is very large or when the source resistance is very small compared to the load resistance. For example, when Rs = 0.5 Ω, and RL = 20 Ω, most of the voltage drop occurs across the load only (VL= 9.76 V) as compared to a voltage drop of only 0.24 V across the source. Table 3.3 also contains the power dissipated in the load resistance and the efficiency of power transfer. The power transferred to the load is maximum when Rs = RL. In the present example, the maximum power transferred is 50 W when RL = Rs= 0.5Ω. On the other hand, the efficiency of power transfer increases when RL becomes much larger than R.
In practical applications, the problem of high efficiency and maximum power transfer is resolved depending on the application. Where the quantities of power involved are large and the efficiency should be high, the load resistance is made large compared to the source resistance, so that losses are kept small. On the other hand, if the load resistance has to be matched to the source resistance, as in communication circuits, to obtain a strong signal then to get high efficiency, the source and load resistance are made equal. In this case, the power transmission will be maximum, whatever the source is capable of supplying.
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