So, looking at the diagram, let us
assume that “I” is the current measured on A.
From
simple circuit equations and use of Kirchhoff’s law, we
determine that:
And also from analyzing the diagram, we determine that:
And finally from that, we can determine the power of the circuit, which is:
If we are to combine the first and third equation, then we will obtain a more usable equation:
With just a quick look at this new equation, we can notice that either a large R resistance or a
small one will make the power approach zero.
Now, to obtain the maximum value for power, the
resistance needs to be at some moderate value.
This means that the maximum power is obtained
when R=r.
This is known as the load being “matched” to the seat of the emf.
Procedure:
This is actually a quite simple lab.
Start off by setting up the circuit so that it matches the
diagram above in the theory section.
Then we will set the external resistance to 300 ohms.
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 Spring '12
 Dr.Phaneuf
 Physics, Resistance, Volt, Electrical resistance, Voltage drop

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