An electrical circuit for measuring the value of a resistance. In the illustration, R1 is a resistance of unknown value, R2 is a fixed resistance of known value, and R3 and R4 are variable resistances with known values. When no current flows between A and B the bridge is said to be balanced, the galvanometer registers no deflection, and R1/R2=R3/R4. R1 can therefore be calculated. The Wheatstone bridge is used in various forms. In the metre bridge, a wire 1 metre long of uniform resistance is attached to the top of a board alongside a metre rule. A sliding contact is run along the wire, which corresponds to R3 and R4, until the galvanometer registers zero. Most practical forms use one or more rotary rheostats to provide the variation. The device was popularized, though not invented, by Sir Charles Wheatstone.
Wheatstone bridge.
A four-arm bridge used for measuring resistance. Each arm contains a resistance (see diagram), with the unknown and reference resistances, R1 and R2, being connected at a point. At balance, when a null response is obtained from the indicating instrument,
The two arms R3 and R4 are known as the ratio arms and may take the form of a wire of uniform resistance, which is tapped by a sliding contact. R3 and R4 are proportional to the lengths of wire, l1 and l2, on each side of the contact, so that
Wheatstone bridge
- Harrison, William Henry (1773–1841)
- Harrod-neutral technical progress
- Harrod–Domar growth model
- Harrop formula
- Harsha (590–647)
- hartebeest
- Hartebeesthoek Radio Astronomy Observatory
- Hartford Convention (1814–15)
- Hart, Herbert Lionel Adolphus (1907–92)
- Hartley, David (1705–57)
- Hartley, Herman Otto (1912–80)
- Hartley oscillator
- Hartley test
- Hartline, Haldan Keffer
- Hartmann, Eduard von (1842–1906)
- Hartmann, Johannes Franz
- Hartmann, Nicolai (1882–1950)
- Hartmann test
- Hartree–Fock procedure
- Hartree–Fock theory
- Hartsfield, Henry Jr (1933–2014)
- Hartshorn bridge
- Hartshorne, Charles (1897–2000)
- Hart, Terry Jonathan (1946– )
- Haruka