# Maximum power is transferred when load R = Source R ?

• jaus tail
In summary, the maximum power theorem states that power is maximized when there are zero source losses. This is met when RL = RS.
jaus tail

## Homework Statement

Maximum power is transferred to variable load when:
1) RL = Rs
2) RL not equal to 0. and Rs = 0
3) RL = 0 and Rs not equal to 0
4) RL = Rs/2

## Homework Equations

Maximum power theorem RL = Rs

## The Attempt at a Solution

But if Rs = 0, then current is maximum, so load get maximum power. Shouldn't answer be B. Book answer is A.
I tried with a 4V dc source and 1 ohm source resistance and 1 ohm load resistance.
Power = 2^2 / 1 = 4.
In second case I put source resistance = 0.
Power = 4^4 = 16.

OK, so with Rs equal to zero, what value of RL gives you maximum power to the load?

jaus tail
With Rs = 0, RL can be whatever is needed. That depends on load requirement. Max power = V2 / RL. Oh yeah. max power is when RL = 0, which is Rs

I guess if RL is not variable when Max power is when Rs = 0.

lol when Rs = 0, max power is infinite and everything goes boom :D

scottdave
jaus tail said:
Maximum power is transferred to variable load when:
1) RL = Rs
2) RL not equal to 0. and Rs = 0
3) RL = 0 and Rs not equal to 0
4) RL = Rs/2
Are you quoting this fully & accurately? If so, then the question gives no indication what they might mean by the terms RL and RS?

Making likely assumptions, (2) is undoubtedly correct. Load power is maximised when there are zero source losses.

jaus tail
Yes the question is same except: Max power is transferred to variable load from source when

But the books have clear indication as to what is Rs and RL

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It seems like a trick question.

jaus tail
You haven't fully addressed scottdave's question. Suppose RS is zero ohms, describe the value of load that will make the load as hot as possible.

NascentOxygen said:
You haven't fully addressed scottdave's question. Suppose RS is zero ohms, describe the value of load that will make the load as hot as possible.
For max power, maximum current which means RL should be zero. Short circuit.
This value matches of Rs = 0.

Certainly, as resistance approaches zero, power approaches infinity. I'm not sure how to view the exactly zero ohms case.

There's a big difference between delivering maximum power to the load (as many watts as possible), and delivering maximum proportion of power to the load (i.e., maximum efficiency; lowest loss in source). The former is met by RL = RS, the latter by setting RS=0 (or RL » RS).

donpacino, anorlunda and jaus tail
Book says right answer is A.
Yeah you're right. For max efficiency, Rs = 0.

NascentOxygen said:
There's a big difference between delivering maximum power to the load (as many watts as possible), and delivering maximum proportion of power to the load (i.e., maximum efficiency; lowest loss in source). The former is met by RL = RS, the latter by setting RS=0 (or RL » RS).

There's a fun anecdote about that difference. When Thomas Edison started the first electric power company, he set RS=0. The electrical engineering societies called him an ignorant fool because they all knew that maximum power is transferred when RS=RL. But those engineers were used to working with a battery where VS and RS are fixed. Edison knew that with his generator, he could adjust VS to be anything he wanted. Edison also knew that the proper question is not maximum power to the load but rather minimum power lost in the source.

donpacino
NascentOxygen said:
There's a big difference between delivering maximum power to the load (as many watts as possible), and delivering maximum proportion of power to the load (i.e., maximum efficiency; lowest loss in source). The former is met by RL = RS, the latter by setting RS=0 (or RL » RS).

As an undergraduate student I had trouble understanding this at first. I remember debating with my professor the exact point jaus tail was trying to make.

donpacino said:
As an undergraduate student I had trouble understanding this at first. I remember debating with my professor the exact point jaus tail was trying to make.

If only our teachers could say it as succinctly and clearly as @NascentOxygen did.

jaus tail

## What is maximum power transfer?

Maximum power transfer is a concept in electrical engineering that refers to the condition where the maximum amount of power is transferred from a source to a load.

## Why is it important?

Maximum power transfer is important because it allows for the efficient use of electrical energy. When the load resistance is matched to the source resistance, the maximum amount of power is transferred, minimizing energy loss and maximizing efficiency.

## What is the relationship between load resistance and source resistance?

The relationship between load resistance and source resistance is that when they are equal, maximum power is transferred. This is known as the maximum power transfer theorem.

## What happens if the load resistance is greater than the source resistance?

If the load resistance is greater than the source resistance, the power transfer will be less than the maximum. This is because some of the energy will be lost as heat in the source resistance, reducing the overall efficiency.

## Can the maximum power transfer condition be achieved in real-world circuits?

Yes, the maximum power transfer condition can be achieved in real-world circuits. However, it may not always be practical or desirable to do so. In some cases, a lower power transfer may be more efficient or may be necessary for the circuit to function properly.

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