Wheatstone bridge
= Wheatstone bridge
{c}
{wiki}
The Wheatstone bridge has four <resistor> arms and two diagonals. Here the supply holds node $A$ at constant <electric potential difference> $V_s>0$ relative to node $D$, our <electrical reference potential>. The left path is $A\to R_1\to B\to R_2\to D$; the right path is $A\to R_3\to C\to R_x\to D$. The unknown is $R_x$, and $R_3$ is adjustable. A <voltmeter> or <galvanometer> connects $B$ to $C$. We define its positive reading as $V_B-V_C$; exchanging its leads reverses the sign. All four <electrical resistances> are positive, the supply is ideal, and the calculation describes steady <electric currents> at fixed <temperature>.
\Image[/wheatstone-bridge-circuit-and-thevenin-equivalent.png]
{title=Four labeled Wheatstone bridge arms and the equivalent circuit seen by the detector}
{id=wheatstone-bridge-circuit-and-thevenin-equivalent}
{description=The supply spans $A,D$; the detector spans $B,C$ and reads $V_B-V_C$. The right panel uses <Thévenin's theorem> to replace the bridge by its open-circuit <electric potential difference> and a series <electrical resistance>.}
{source=wheatstone-bridge-circuit-and-thevenin-equivalent.py}
<Charles Wheatstone> described the instrument in his 1843 Bakerian lecture while explicitly crediting <Samuel Hunter Christie>. The account from King's College London's collection identifies that attribution; the familiar name should not be read as an assertion that Wheatstone alone originated the bridge.<Wheatstone Collection by King's College London>[Wheatstone Collection, section “Wheatstone's contributions to electricity”: 1843 lecture and credit to Samuel Hunter Christie]{ref}