Wheatstone Bridge & Meter Bridge — A/L Physics

What must I remember about Wheatstone Bridge & Meter Bridge?

• Wheatstone Bridge Circuit: Bridge network of four resistors P, Q, R, S connected in a diamond with galvanometer G across central branch and emf source E across outer corners.
• Bridge Balance Condition: When no current flows through galvanometer (I_g = 0, null deflection): Potential at node B equals node D (V_B = V_D); Balance Condition: P / Q = R / S.
• Meter Bridge (Slide-Wire Bridge): Practical realization of Wheatstone bridge using a uniform resistance wire of length 100 cm: Unknown resistance X / Known resistance R = L1 / (100 - L1).
• End Corrections: Small resistances arising from copper end strips and soldering joints at wire ends (0 cm and 100 cm marks); eliminated by interchanging known resistor R and unknown X and averaging.

Test yourself (1 minute)

1. Maximum Sensitivity of Wheatstone Bridge

   Bridge sensitivity is maximized when all four arms have roughly equal resistance values (P ≈ Q ≈ R ≈ S); balance point on Meter Bridge is most accurate near center (L1 ≈ 50 cm).

2. Zero current independence

   At balance (I_g = 0), the balance condition P/Q = R/S is completely independent of the galvanometer's internal resistance and the battery's emf/internal resistance.

3. Interchanging Battery and Galvanometer

   Interchanging the positions of the battery and galvanometer does not affect the balance condition.

Practise Wheatstone Bridge & Meter Bridge questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 7: Current Electricity

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Where does Wheatstone Bridge & Meter Bridge fit in the syllabus?

Unit 7.7 · Year 2 · Term 1