# Homework Help: Circuit Problems : Finding Current and Voltage

1. Aug 4, 2011

### gatsbycollege

1. The problem statement, all variables and given/known data
The Circuit is given as shown in the figure
http://img215.imageshack.us/img215/8361/circuitsl.jpg [Broken]

find V,
V, = ranging from 78v - 90v

2. Relevant equations
KVL
E=E1+E2+E3...+En
KCL
I=I1=I2
Ohms Law
V=IR

3. The attempt at a solution
i used KVL
72v-2000ohms(i)-0.5V,-V,=0
then i have this equation
72v=1.5V, +2000i (1)

in the 2nd resistor with 3000ohms
i derived the equation
V,=(2I)(3000ohms)
so V,=6000ohmsi (2)

substitution in eq (2) and (1)

i=0.007A

then going back to eq (2)
V,=42v <---- but this is not correct by looking at the range my prof gave me..
so i think i missed something here or my whole idea is not correct..
btw i dont really know if that 2i is in series with the resistor 3000ohms
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited by a moderator: May 5, 2017
2. Aug 4, 2011

### Staff: Mentor

Where does the extra "-V," come from at the end? When I follow a KVL path around the first loop I go through the 72V source, the 2000Ω resistor, then the "0.5V," source and then back to the beginning via path AB.

3. Aug 4, 2011

### gatsbycollege

whew that solve my problem.. that "-V," is not included XD