hi everyone.

I need some help in understanding some details of kelvin's bridge.

What many sites have told me is that potential difference between a and b is the same as that between ac. How is that possible since the voltage between ab is actually a fraction of the voltage ac(since it is a voltage divider.)

One of the sites offered a more logical explanation which said that voltage ab is equal to voltage ad and used math to prove it.

Also why do we need the r wire. Cant we just make do by connecting m and n up close to the resistors to decrease the effect of wire resistence.

thanks for help