Wheatstone bridge

(noun)

An instrument used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.

Related Terms

Examples of Wheatstone bridge in the following topics:

  • Null Measurements

    • The Wheatstone bridge is a null measurement device for calculating resistance by balancing potential drops in a circuit.
    • The device is called a bridge because the galvanometer forms a bridge between two branches.
    • A variety of bridge devicesare used to make null measurements in circuits .
    • The Wheatstone bridge is used to calculate unknown resistances.

  • Control of Muscle Tension

    • Muscle tension is influenced by the number of cross-bridges that can be formed.
    • Neural control initiates the formation of actin–myosin cross-bridges, leading to the sarcomere shortening involved in muscle contraction .
    • The number of cross-bridges formed between actin and myosin determine the amount of tension that a muscle fiber can produce.
    • Cross-bridges can only form where thick and thin filaments overlap, allowing myosin to bind to actin.
    • If more cross-bridges are formed, more myosin will pull on actin and more tension will be produced.

  • ATP and Muscle Contraction

    • ATP is critical for muscle contractions because it breaks the myosin-actin cross-bridge, freeing the myosin for the next contraction.
    • As soon as the actin-binding sites are uncovered, the high-energy myosin head bridges the gap, forming a cross-bridge.
    • After the power stroke, ADP is released, but the cross-bridge formed is still in place.
    • ATP can then attach to myosin, which allows the cross-bridge cycle to start again; further muscle contraction can occur.
    • The cross-bridge muscle contraction cycle, which is triggered by Ca2+ binding to the actin active site, is shown.

  • Velocity and Duration of Muscle Contraction

    • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
    • However, cross-bridge formation is not immediate and if myofilaments slide over each other at a faster rate, their ability to form cross-bridges and subsequent force are both reduced.
    • At a maximum velocity no cross-bridges can form so no force is generated, resulting in the production of zero power (right edge of graph).

  • Turbulence Explained

    • It is imperative to consider turbulent flow when designing many things such as airplanes, medical equipment, heat exchangers, and bridges.
    • It is imperative to take into account turbulent flow when designing certain structures, such as a bridge support, as shown in .
    • The bridge supports must be designed so that they can withstand the turbulent flow of the water in the spring.
    • Turbulent flow is visible around the bridge supports of the Longtown bridge.

  • Regulatory Proteins

    • Tropomyosin blocks myosin binding sites on actin molecules, preventing cross-bridge formation, which prevents contraction in a muscle without nervous input.
    • Once the tropomyosin is removed, a cross-bridge can form between actin and myosin, triggering contraction.
    • Cross-bridge cycling continues until Ca2+ ions and ATP are no longer available; tropomyosin again covers the binding sites on actin .
    • The outflow of calcium allows the myosin heads access to the actin cross-bridge binding sites, permitting muscle contraction.
    • Cross-bridge cling continues until the calcium ions and ATP are no longer available.

  • Force of Muscle Contraction

    • When a sarcomere contracts, myosin heads attach to actin to form cross-bridges.
    • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
    • However, cross-bridge formation is not immediate, so if myofilaments slide over each other at a faster rate the ability to form cross bridges and resultant force are both reduced.
    • At maximum velocity no cross-bridges can form, so no force is generated, resulting in the production of zero power (right edge of graph).

  • RBL Knowledge-Check

    • This game was created by Jenny Bridges, Carrie Davison, and Karen Hymas (Fall, 2008).

  • Cast-Iron Architecture

    • Cast iron was also used widely in bridge construction for the new railway system, sometimes with horrific results, especially when cast iron girders were used instead of arches.
    • The most serious accident occurred in 1879 with the Tay Bridge disaster, when the center part of the bridge collapsed in a storm as an express train was passing over .
    • The weakest parts of the bridge were cast iron lugs holding tie bars in place, and cast iron in new bridges was effectively abandoned after the disaster.
    • The Tay Bridge, one of the major cast-iron architecture disasters, after the 1879 collapse of the mid-section during a storm as an express train was passing over.
    • This image illustrates the original Tay Bridge before the 1879 collapse.

  • Short-Term Loans

    • In December 2010, Kohlberg Kravis Roberts (KKR) and partners marketed a bridge loan for its upcoming acquisition of Del Monte Foods.
    • A bridge loan is a type of short-term loan, typically taken out for a period of two weeks to three years pending the arrangement of larger or longer-term financing.
    • Money from the new financing is generally used to "take out" (i.e. to pay back) the bridge loan, as well as other capitalization needs.
    • Bridge loans are typically more expensive than conventional financing to compensate for the additional risk of the loan.
    • Bridge loans are used in venture capital and other corporate finance for several purposes: