maximum power transfer

[bhuvanesh]

if u have 8 ohm load resistance(speaker) in series (voltage divider circuit) with another resistor(?)

what resistance do u choose same 8 ohm as load or less or high
i have heard by many to choose same but i dont know reason.plz explain me detially.thank you in advance

 

[Laplace]

Have you calculated the power transferred in your circuit for a range of resistor values and plotted the result on a graph? Or better yet, derive the power transfer expression as a function of the resistor value then take the derivative with respect to the resistance and look for the point of inflection where dP/dr=0. Does the differential calculus answer your question?

 

[bhuvanesh]

thanks for your response.first clear one thing,in voltage divider bias.if you want to transfer maximum power to load resistance(simply a resistor)what you do.does you choose the source resistance small or same as load resistance(simply resistor).thanks in advance

 

[BobK]

Putting a resistor in series with a speaker will always reduce the power to the speaker. So what resistance will reduce it the least?

Bob

 

[Electrobrains]

thanks for your response.first clear one thing,in voltage divider bias.if you want to transfer maximum power to load resistance(simply a resistor)what you do.does you choose the source resistance small or same as load resistance(simply resistor).thanks in advance

Does this trace belong in the "Homework section"...?
I think Laplace has given the perfect hint. Try the derivation of the Power function!
Basically it doesn't matter if the resistors are seen to be outside or inside the source.

 

[BobK]

Finding a zero in the derivative will not help in this case. The max will be at an endpoint.

I think the question is phrased wrongly. The way it is phrased, putting a resistor in series with a speaker, the answer of what resistor will result in the most power transfer (to the speaker presumably) is obvious.

Bob

 

[Arouse1973]

For optimum power transfer to a load you have to match the source resistance with the load resistance this is 50% power. If you change the load resistance up or down this reduces the power in the load and either increase it or decrease the power in the source resistance. SqrtRs/ SqrtRL = 1 so Rs must equal RL.

Adam

 

[BobK]

But that is not what he asked. He is asking about putting a resistor in series with the speaker, then presumably connecting it to an amp. You will get the most power to the speaker with 0 Ohms as a series resistor. I think he really wanted to ask what you are answering, but phrased it badly.

The only way the equal resistance is optimal is if you have a voltage source with a given output impedance that you cannot change. For most real amps, this will be a fraction of an Ohm. With is why you get more power into a 4 Ohm speaker than an 8 Ohm one on a typical amp.

Bob

 

[Arouse1973]

Yes Bob but I read between the lines as I think I know what he meant.

 

[bhuvanesh]

thanks bobk.u meant to use active device instead of resistor.so the load does not bend .could u explain a little bit how it will be optimal if we use op amp.please.and really thanks bob

 

[BobK]

Arouse,

I hate to belabor the point, but I can't see that the answer (an equal resistor) is possible for the question he asked. He is talking about a speaker of fixed impedance in series with a resistor that you can choose. If you can choose the resistor, the answer is always 0. The answer you give is for a different question. Given a voltage source with a fixed impedance, what load resistor would result in the maximum power in the load. This might indeed be the question his professor was asking, but perhaps it is not and I cannot see that from the way the OP was phrased.

Bob