# Choose a voltage V <2.5 V

1. Sep 9, 2012

### Mosaness

1.Choose a voltage v < 2.5 V and values for the resistors R1, R2, R3, and R4 in
the circuit of Fig. 3.90 so that i1 =1 A, i2 =1.2 A, i3 =8 A, and i4 = 3.1 A.

2. Relevant equations

KCL/KVL/OHms Law

3. The attempt at a solution

If Is = I1 + I2 + I3 + I4,

Then, Is = $\frac{v}{Req}$

Req = $\frac{1}{R1}$ + $\frac{1}{R2}$ + $\frac{1}{R3}$ + $\frac{1}{R4}$.

After this, I get stuck...

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2. Sep 9, 2012

### Bhumble

You're over thinking the problem. For parallel branches, the voltage is the same to all branches of the node. For simplicity choose 1V and for R1 choose 1 ohm so that I1 = 1A. Now you have the voltage and current for each branch so just solve for resistance via ohm's law.

3. Sep 9, 2012

### Mosaness

So because we can choose any v that is less than 2.5V, you picked 1V correct?

4. Sep 9, 2012

### Mosaness

Taking V as 1A and using the given values for the currents, I solved for R1, R2, R3, and R4:

R1 = 1V/1A = 1Ω

R2 = 1V/1.2A = 0.83Ω

R3 = 1V/8A = 0.125Ω

R4 = 1V/3.1A = 0.323Ω

Is this correct?

5. Sep 10, 2012

### Bhumble

Looks good. And if for some reason you need the voltage to be higher than you can just scale the resistance proportionately to maintain the same current.