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Question 7: Describe that maximum power is transferred when the impedance’s of source and load match to each other.


Theorem of maximum power transfer

It states that for transferring the maximum power from the source to the load, the load impedance should match the source impedance. Mathematically, if RL is the load resistance and Ri is the source resistance, then RL = Ri.

Consider the figure of a simple source and load circuit. The source may be an AC or DC one. Its internal resistance drives a load resistance.

We know that

see section 12.14, chapter 12

Put R = RL and r = Ri, the equation becomes,

From this equation, it is clear that power will be maximum if the fraction on the RHS has maximum value. This is possible, however, when RL – Ri = 0 which means that RL = Ri.

Therefore, maximum power will be transferred to the load if the load impedance and the source impedance are equal.

The adjacent graph shows that matching source and load impedances gives maximum power.

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