Final answer:
To construct a circuit model, find the equivalent resistance Rp using Ohm's Law and the sum of individual currents flowing through the resistors. To find the required resistance r, subtract Rp from V divided by the sum of the currents produced by the source.
Step-by-step explanation:
To construct a circuit model for the device using an ideal current source in parallel with a resistor, we need to find the required resistance, r. Let's consider the currents flowing through the circuit. Since each resistor has the full voltage, the currents flowing through the individual resistors can be represented as I1 = V / R1, I2 = V / R2, and the current produced by the source is the sum of these currents: I = I1 + I2 + I3.
To find the equivalent resistance of the circuit, Rp, we can use Ohm's Law. Since the current produced by the source is the sum of the currents through the individual resistors, I, we can write: I = V / Rp. Rearranging the equation, we can find the required resistance, r: r = V / I - Rp.