Homework Help: Design a Circuit

1. Jul 29, 2014

Zondrina

1. The problem statement, all variables and given/known data

You are given two ideal batteries with $\epsilon_1 = 1.5 V$ and $\epsilon_2 = 9.0 V$. You are also given three $120 \Omega$ resistors.You may use any or all of the components. Design a circuit where there is a current of $21 \pm 1 mA$ through at least one of the resistors.

Do NOT use EMF sources in parallel.

2. Relevant equations

3. The attempt at a solution

I've already tried several combinations of resistors and batteries with no avail. The closest I've been is when all three resistors are in series with the $9.0 V$ emf. Then the current across the whole circuit is $25 mA$. I've also tried creating several multiloop circuits, but those haven't worked either.

Anyone have some design advice? It would be very appreciated.

EDIT: Never mind guys I got it, just place the resistors in series and then oppose the emfs. Then the current is $\frac{9.0-1.5}{360} = 21 mA$.

Last edited: Jul 29, 2014
2. Jul 29, 2014

phinds

glad to see you got it. I've never understood the utility of such problems, they just seem silly to me but I've seen them before.