# Homework Help: Voltage and current calculation on a mixed circuit

1. Nov 23, 2008

### sylvarant

1. The problem statement, all variables and given/known data
I have the following circuit
http://informatici.vankeer.eu/files/2/Untitled.png

R1 = 22 ohm, R2 = 39, R3 = 82, R4 = 100,R5 = 10
and V = 2volt

I'm asked to calculate the voltage and current over de resistors

when the switch is open and when the switch is closed

2. Relevant equations
when 2 resistors form a combination the current is the same and V = IR

when 2 resistors are in parallell there voltages are the same and Ii = V/Ri

3. The attempt at a solution
well when the switch is open I obtain the following
the resistors R1 and R4 form a combination and so do R2 and R3 the voltage remains equal for both combinations so we can easily calculate the current
I1=I4 = 2v/(22+100)ohm = 0.016 A
now we find the voltage over both resistors
V1= 0.016 * 22 = 0.361 Volt
v4 = 0.016 * 100
Same way for I2 and I3

But I'm stuck when the switch is closed how do I calculate the current and voltage then ?

2. Nov 23, 2008

### ptr

It might be well to read up on "Delta-Wye" transformations.

3. Nov 23, 2008

### Staff: Mentor

Have you learned how to write KCL equations yet? Write the two KCL equations for the left and right nodes, and solve for the two unknowns V(left node) and V(right node).
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