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  #1  
Old 01-06-2012, 09:05 PM
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PG1995 PG1995 is offline
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Default ac analysis: maximum power transfer

Hi

Please have a look on the attachment. Please help me with the query. Thanks a lot.

Regards
PG
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File Type: jpg maxpowersingle.jpg (168.0 KB, 27 views)
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  #2  
Old 01-06-2012, 09:52 PM
steveb steveb is offline
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Originally Posted by PG1995 View Post
Hi

Please have a look on the attachment. Please help me with the query. Thanks a lot.

Regards
PG
Actually, if XL=-Xth, then RL=Rth. If you substitute eqn. 17 into eqn. 18 then it automatically follows.
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Old 01-07-2012, 09:41 AM
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Thank you.

I'm sorry I thought the author was simply adding them up... It's not that I haven't asked such dumb questions before!

Best wishes
PG
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Old 01-07-2012, 01:05 PM
steveb steveb is offline
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Thank you.

I'm sorry ... It's not that I haven't asked such dumb questions before!
You're welcome.

Actually, you haven't asked any question as dumb as that. But, everyone has to own a dumbest question, and there are much worse ones to own than that.

I'm too embarrassed to tell you mine!

Anyway, mistakes and oversights are committed the best of us, and sometimes more often by the best of us, so don't be sorry.
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  #5  
Old 01-07-2012, 03:16 PM
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PG1995 PG1995 is offline
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Actually, you haven't asked any question as dumb as that.


You are so nice. That's true that you are not infallible despite being very knowledgeable, as Mrs. Steve thinks you mentioned once, but one thing is true that you are one of the nicest persons I have come across. Actually this forum is full of so many nice members who are willing to help without ridiculing you or making fun of your questions.

With best wishes
PG

Last edited by PG1995; 01-07-2012 at 06:48 PM.
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  #6  
Old 01-13-2012, 01:22 PM
tony caney tony caney is offline
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Default Rl=rth

The RTH is the Thevenin equivalent cct for maximum power transfer
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  #7  
Old 01-14-2012, 08:24 PM
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Default average power, ac power analysis

Hi

Please have a look on the attachment. Please help me with the query. Thank you.

Regards
PG
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File Type: jpg averagepowersingle.jpg (225.6 KB, 7 views)

Last edited by PG1995; 01-14-2012 at 08:30 PM.
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Old 01-14-2012, 10:15 PM
steveb steveb is offline
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Hi

Please have a look on the attachment. Please help me with the query. Thank you.

Regards
PG
Double check your complex math calculation. Magnitude squared is indeed found by multiplying by the complex conjugate. But, the answer always comes out to a real number, if you do the math without errors.

(2+7i)(2-7i)=4+14i-14i+49=53
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  #9  
Old 01-15-2012, 02:11 PM
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Default IrwinExt9.1

Hi

Please have a look on the attachment. Please help me with the query. Thank you.

Regards
PG
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Old 01-15-2012, 05:06 PM
steveb steveb is offline
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Hi

Please have a look on the attachment. Please help me with the query. Thank you.

Regards
PG
It's not clear to me how you are trying to calculate the power in the capacitor. If you trying to calculate average real power, then you must realize that the voltage and current are always 90 degrees out of phase in either a coil or a capacitor. If you do out the integral for average power over one period, you'll see that the 90 degree phase shift results in the product of voltage and current forming a symmetrical function above and below the time axis. Hence, the integral is zero. So, reactive components (coils and caps) have only reactive power and no real power. Reactive power is just a case of power flowing out and then flowing back in over the course of a period.

The resistor power formula is derived in the same way, but since current and voltage are in phase, the product of the two is always greater than zero, and hence the integral can't be zero unless both voltage and current are zero (EDIT: I meant to say "either" voltage or current is zero).

Last edited by steveb; 01-15-2012 at 08:05 PM.
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