P 5.4-9 A resistor, R, was connected to a circuit box as shown in Figure P 5.4-9. The current, i, was measured. The resistance was changed, and the current was measured again. The results are shown in the table.

(a) Specify the value of R required to cause i = 2 mA.

(b) Given that R > 0, determine the maximum possible value of the current i.

Hint: Use the data in the table to represent the circuit by a Thévenin equivalent.

Figure P 5.4-9

Assume the circuit is a Thevenin circuit we would have the following

We would find the current from

Plug in the two data points given

and

Rearrange equations and we have two equations and two unknowns

Since is the same we can write

Solve for

And is

So the circuit is

(a) Specify the value of R required to cause i = 2 mA.

Solve for R

(b) Given that R > 0, determine the maximum possible value of the current i.

Since

i is maximized when the denominator is minimized, so make R = 0 and you would have greatest possible i

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