# help with Wheatstone Bridge

Thread Starter

#### terrakota

Joined Feb 8, 2005
67
Hi,

I'm trying to find the voltage betwen point A and B(the point that must be 0 to be the bridge balanced) I know i must use the voltage divider formula to find voltage from point A to ground ie. 3V, then i calculate the point B to ground voltage and is ie. 2v, to find the voltage betwen this 2 points i must substract 3v-2v = 1v.

why i substract v1 from v2 and not v1+v2, or v1/v2? whats the theory why this 2 voltages must be substractedand not added or divided?

thanks for any help
and please excuse my poor english

#### mozikluv

Joined Jan 22, 2004
1,437
hi

if you have actually build the bridge and actually got the result and confirmed by the formula you can already deduced why you it's not add or divide.

#### kshtron

Joined May 29, 2005
2
Originally posted by terrakota@May 18 2005, 08:54 PM
Hi,

I'm trying to find the voltage betwen point A and B(the point that must be 0 to be the bridge balanced) I know i must use the voltage divider formula to find voltage from point A to ground ie. 3V, then i calculate the point B to ground voltage and is ie. 2v, to find the voltage betwen this 2 points i must substract 3v-2v = 1v.

why i substract v1 from v2 and not v1+v2, or v1/v2? whats the theory why this 2 voltages must be substractedand not added or divided?

thanks for any help
and please excuse my poor english
[post=7794]Quoted post[/post]​
Hi,
If you think of the two series paths from power to ground as two seperate circuits and calculate the voltage drop from the top of the grounded resitor (A and B) of each circuit to ground you will get different values in an unbalanced bridge. When both values are the same the bridge is balanced. Recall that voltage is defined as a difference of potential between two points. By subtracting the voltage between points A and B we establish the voltage between those points. By the way the sign only indicates direction of current flow. maybe this will help; I hope so.

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