The voltage between two points

[Eman 5]

Homework Statement

I want to know the voltage between a and b in the drawing below.[/B]

Homework Equations

V= IR

The Attempt at a Solution

The resistors 5Ω and 5Ω are in series:
(Req)1= 5+5=10Ω
The resistors (Req)1, 5Ω and 10Ω are in parallel:
1/(Req)2= 1/10+1/5+1/10=2/5
(Req)2=2.5Ω
The resistors (Req)2 and 2.5Ω are in series:
Rt=2.5+2.5=5Ω
I=V/Rt=15/5=3A
The voltage between a and b= IR
I have I but I don't know how to get R between the two points.

 

[kuruman]

Edited: Start by finding the total current put out by the battery. Then consider the voltage drop across the 2.5 Ω resistor.

 

[Asmaa Mohammad]

@Eman 5
You should know that iR, in this case, is the voltage drop between any branch in the circuit you drew, i.e. you can consider any branch of them to determine the voltage drop (potential difference) between the points a and b, because all branches in this circuit are connected to the points a and b.

For example, consider the above branch which has the battery and the 2.5 ohms resistance. Remember that the current passing through that branch is 3A.

Now determine the potential difference through that branch.

 

[Eman 5]

The voltage across 2.5Ω resistor=IR=3×2.5=7.5V
The voltage drop across the above branch= 15−7.5=7.5V
Is this correct?

 

[cnh1995]

The voltage across 2.5Ω resistor=IR=3×2.5=7.5V
The voltage drop across the above branch= 15−7.5=7.5V
Is this correct?

Yes.