Hi!
How can I calculate in this case the voltage between A and B?
Thanks for help.

 

hi zg,
Welcome to AAC.
As it is homework, please show your attempt at solving the problem, then we can then guide you.
E

 

hi zg,
Welcome to AAC.
As it is homework, please show your attempt at solving the problem, then we can then guide you.
E

I made this schematic design from the circuit and calculated the currents using the Kirchhoff's laws, but I don't know how to get the voltage between A and B.

 

I made this schematic design from the circuit and calculated the currents using the Kirchhoff's laws, but I don't know how to get the voltage between A and B.
View attachment 160513

Hint:
In your case, you can safely assume that the XMM1 has infinite resistance.

 

I made this schematic design from the circuit and calculated the currents using the Kirchhoff's laws, but I don't know how to get the voltage between A and B.
View attachment 160513

What did you get for the currents?

Remember that if Vxy means the voltage from Node X to Node Y, then

Vxy = Vx - Vy

Also note that this means that

Vyx = Vy - Vx = -Vxy

Thus, if you have Nodes A, B, C, D, and E, you can write things such as

Vac = Va - Vc = Va - Vb + Vb - Vc = Vab + Vbc

You can generalize this to

Vae = Vab + Vbc + Vcd + Vde

All this really means is that you can calculate the voltage between any two points by walking any path between those points and adding the voltages as you go.

So call the node below R2 Node C and the node below R3 Node D.

If you've calculated I3 and I5, can you find Vac and Vbd? What is Vdc?

If you know those, can you find Vab?

Also, the symbols you have for the batteries is counter to the normal symbols (at least used most places) which have the short line side as the negative terminal.

 

One point that needs to be clarified is deciding which side of the battery should be considered as positive. In the scematic the + sign is against the side of the battery symbol that is normally considered as negative.

Les.

 

What did you get for the currents?

Remember that if Vxy means the voltage from Node X to Node Y, then

Vxy = Vx - Vy

Also note that this means that

Vyx = Vy - Vx = -Vxy

Thus, if you have Nodes A, B, C, D, and E, you can write things such as

Vac = Va - Vc = Va - Vb + Vb - Vc = Vab + Vbc

You can generalize this to

Vae = Vab + Vbc + Vcd + Vde

All this really means is that you can calculate the voltage between any two points by walking any path between those points and adding the voltages as you go.

So call the node below R2 Node C and the node below R3 Node D.

If you've calculated I3 and I5, can you find Vac and Vbd? What is Vdc?

If you know those, can you find Vab?

Also, the symbols you have for the batteries is counter to the normal symbols (at least used most places) which have the short line side as the negative terminal.

Now I can solve it.
Thanks for the help.