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posted by  Bebeto on 11/5/2009 2:59:10 PM  |  status: Closed  |  Earned Karma: 53

Finding R load

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Electrical Engineering N/A N/A N/A 12/5/2009 at 3:00:00 PM
Question Details:
Hello you guys. This is a two part assignment and I already did the 1st questions i just need some help on the second part.   The origianl circuit is below:

   

For the fist question they asked for the thevenin equivalent so this is what i got:


And this is the question I'm having trouble with: For the above circuit find the value of Rload where maximum power transfer will occur and the value of that power.

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posted by Tachyon12 on 11/5/2009 3:13:29 PM  |  status: Live
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Response Details:
To find the maximum power transfer, u need to know the Maximum Power Transfer theorem.

The maximum power transfer theorem states that, to obtain maximum external power from a source with a finite internal resistance, the resistance of the load must be made the same as that of the source.

So the maximum power will be absorbed by Rload, when Rload=1.75kΩ

The maximum power absorbed by Rload=Vload x Iload = 2.5 x 5/3.5 =3.57mW
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posted by UD117 on 11/5/2009 4:08:49 PM  |  status: Live
Asker's Rating: Somewhat Helpful   
Response Details:
to find the maximum power you need the resistance from your thevinin circuit to equal the R load
you cause you the formula  p = i^2 * R
the max power you can get is 1.75kOhms(i did not get a chance to calculate the thevini equivalent but it looks good at first glance)
get the current through ohms law i = V/R  i = 2.85 mA
plug the numbers in power= (2.85mA)^2 * 1.75kohms   = .01428W which is 14.28 mW
*note the guy above me messed up using the ohms law he put R= V * I  which makes no sense because the ohms law states V= RI
please rate thanks
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