- #1

Pouyan

- 103

- 8

- Homework Statement:
- In the circuit shown below, I will determine the voltage between points P and Q. The answer is given but my problem is that I can not find the total resistance in the circuit.

- Relevant Equations:
- V=R*I

The true answer is : The voltage between P and Q is 1.5 V.

I got stuck finding the total resistance. My question is:

Is B parallel to both A and C?

Is C parallel to D ?

I tried many ways to find the total R but failed!

My first attempt:

I say the system ABD is in serie with C:

$$\frac{1}{R_{A}} +\frac{1}{R_{B}} + \frac{1}{R_{C}} $$

and $$R_{ABD}=11.54\Omega $$

together with R

_{c}:

$$R_{C}+R_{ABD}=26.54\Omega $$

$$I_{total}=\frac{12}{26.54}\textit{A}=0.45A$$

In this case when Rc is in seire with R

_{ABD}, then the current is the same in both systems and the voltage at R

_{c}= 15*0.45V=6.75V!

The voltage in the ABC is (12-6.75)V = 5.25 V.

The current I

_{A}is then at R

_{A}= $$\frac{5.25}{50} A$$

But it's not correct! since I know that V

_{PQ}=1.5 V!

How can I get the total R ?