Understanding Voltage: A Question on Voltage

[machinarium]

This is what I didn't understand about the picture.
About the -V_R and +V_R, why do we have them, in both directions. I don't understand what they mean. Was A supposed to be more positive than B?

I think I understand voltage and current but I haven't gained insight. That make me confused about this.

 

[n.karthick]

A will be more positive than B if current enters at A i.e, when Ir is positive
The sign of Vr depends on direction of current flow which is depicted in the picture.

 

[Jiggy-Ninja]

Without a bit more context for the picture it's kind of hard to know what it's for. Is this from a textbook or some webpage?

It could be showing the difference between electron and conventional current flow, or that power is still positive if you switch the voltage, or maybe something else I can't think of yet.

 

[vk6kro]

It is showing the difference in voltage polarities between resistors and power sources.

Just looking at the red writing in the diagram at left, the current is flowing downwards and producing a voltage drop across the resistor with the positive voltage being at the point where the current enters the resistor.

If the polarity was as shown in the blue writing (ie -V_R) then the object is a battery or other power source.

It seems to add more confusion than it needs to.

 

[machinarium]

Without a bit more context for the picture it's kind of hard to know what it's for. Is this from a textbook or some webpage?

It could be showing the difference between electron and conventional current flow, or that power is still positive if you switch the voltage, or maybe something else I can't think of yet.

Im sorry about the source. en.wikiversity.org/wiki/Passive_sign_convention
Im confused of the arrows with V and its sign.