Electric Circuits Delta-to-Y and Y-to-Delta Transformation

[annonerjee]

Homework Statement

Three 6 ohm resistors are connected in delta with terminals a, b and c between the resistors.
Determine:
a)The equivalent Y circuit.
b)The resistance between terminals ab in both circuits with terminal c short-circuited to a.
c)Assuming that a 12 V source is connected between terminals ab with terminal c open, calculate the power dissipated in both circuits.

Homework Equations

Delta to Y:
R1=(RbRc)/(Ra+Rb+Rc)
R2=(RaRc)/(Ra+Rb+Rc)
R3=(RaRb)/(Ra+Rb+Rc)
Y to Deta:
Ra=(R1R2+R2R3+R3R1)/R1
Rb=(R1R2+R2R3+R3R1)/R2
Rc=(R1R2+R2R3+R3R1)/R3

The Attempt at a Solution

a) I figured this part out. I used the formula and got that each resistor must equal 2 ohms in the Y equivalent.
I am having trouble with b and c, however.
I part b, after i short circuited a and c, I got that the resistors between ab and bc are in series so the req will be 12 ohms and since the third element is shorted then no current will flow through it. But the answer should be 3 ohms.
For part c I don't even know how to start.
Please help.

 

[n.karthick]

In part B , how you concluded that the resistors are in series? You may draw the circuit diagram and visualize to check whether you are right.

To solve part C also first drawing the circuit diagram and open circuiting terminal C, will enable you to calculate whatever you want.