Thevenin/ Maximum power transfer Theorem.

Thread Starter

Eivhov94

Joined Oct 11, 2013
1
Hi guys!
Can you please help me with this task. I can't agree with myself on what the maximum power transfer will be in this circuit.

Here is the circuit: http://tinypic.com/view.php?pic=2vhyzdh&s=5#.UlfHy1BT538

Task a)
Compute Vth and Rth in this Thevenin-equivalent circuit.

I calculated Vth to be 6 v, and Rth to 6 ohm, and Rs to 2 ohm. .

task b)

Determine R in order to achieve maximum power transfer to it from the rest of the circuit.
Calculate the maximum power transferred.

I calculated P to 40.5w. Is this correct?

Thanks for your help!!
 
Last edited:

Teknolog

Joined Sep 1, 2013
31
For maximum power output, you will want to have the same resistance on the load as the Thevenin equivalent resistance.

I took the liberty of uploading a mathematical explanation (from Hambley):

 
I think it should be equal to 6 Ohms.
With 6 Ohms power dissipated along that resistor = 1.5 Watts.
With 7 Ohms power dissipated along that resistor = 1.49 Watts.
With 5 Ohms power dissipated along that resistor = 1.48 Watts.
 

WBahn

Joined Mar 31, 2012
26,055
Hi guys!
Can you please help me with this task. I can't agree with myself on what the maximum power transfer will be in this circuit.

Here is the circuit: http://tinypic.com/view.php?pic=2vhyzdh&s=5#.UlfHy1BT538

Task a)
Compute Vth and Rth in this Thevenin-equivalent circuit.

I calculated Vth to be 6 v, and Rth to 6 ohm, and Rs to 2 ohm. .
What on earth is Rs? The circuit diagram makes no mention of an Rs. We aren't mind readers -- clearly define or indicate what you mean by the symbols you use.

Are you saying that you used this as your load? Why? How did you come up with that particular value? Show your work. Again, we aren't mind readers.

task b)

Determine R in order to achieve maximum power transfer to it from the rest of the circuit.
Calculate the maximum power transferred.

I calculated P to 40.5w. Is this correct?

Thanks for your help!!
So what value of R did you come up with? Apparently R here is NOT the same as the Rs you had in task a, otherwise you wouldn't be using different names, right? Again, we aren't mind readers.

How did you calculate that power? Show your work! Seeing HOW you got a wrong answer goes a long way to determining WHAT you did wrong. Don't make us guess. We aren't mind readers.

Notice a theme?

Also, start asking if the answer makes sense.

Q1) If you have a 6V source in series with a 6Ω resistor (and further in series with a load resistor Ro), what is the absolute maximum amount of current that can be pulled from the 6V source?

Q2) How much power is the 6V source delivering under these conditions?

Q3) Can it ever deliver more power than that?

Q4) How does that compare with the power you are claiming is delivered to the load?

Q5) What does that tell you about your answer?
 

WBahn

Joined Mar 31, 2012
26,055
I think it should be equal to 6 Ohms.
With 6 Ohms power dissipated along that resistor = 1.5 Watts.
With 7 Ohms power dissipated along that resistor = 1.49 Watts.
With 5 Ohms power dissipated along that resistor = 1.48 Watts.
Please don't just give out answers. Guide the OP toward finding the answer on their own.
 
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