# thevenin and norton

Can someone please guide me on what I need to do to find Rth and IL in the circuit below?
thevnor.JPG
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Commented:
(a) is a voltage divider.  You should be able to write the voltage divider equation and rearrange it to find R_th.

(b) is a classic current divider.  Note that the voltages R_n and R_L are the same.
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Author Commented:
IL = RN/(RN+RL) IN

is this right?
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Commented:
That is correct.
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Author Commented:

find an expression for the gradient of this function, dIL/dRL
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Commented:
That is asking how IL changes as a function of changes in RL.

Maybe they actually want you take the derivative.
But probably you just need to think about the sign of the change.

As RL becomes more positive, what happens to IL??
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Author Commented:
yes...they want me to take the derivative....

but as RL becomes more positive IL becomes smaller
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Author Commented:
is my derivation below correct?

L = [RN/(RN+RL)] IN
dIL/dRL = RN*[-1/(RN+RL)2] IN = -[RN/(RN+RL)2] IN
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Commented:
I believe that is correct.
But my differentiation is much rustier than my network theory.
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Author Commented:
I believe there isn't a minus sign there as well
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Commented:
>> but as RL becomes more positive IL becomes smaller

The minus sign is correct.
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