- Wheatstone Bridge
- Principle of Wheatstone Bridge
- Balanced Wheatstone Bridge
- Unbalanced Wheatstone Bridge
- Applications of Wheatstone Bridge
- Kelvin’s Double Bridge

**Charles Wheatstone**which is used to measure an unknown resistance.

### Principle of Wheatstone Bridge

The Wheatstone bridge principle states that if four resistances P, Q, R and S are arranged to form a bridge with a cell and key between A and C, and a galvanometer between B and D then bridge is said to be balanced when galvanometer shows a zero deflection. In balanced condition$\mathrm{I}_{9}=0 \quad$ so $\mathrm{V}_{\mathrm{B}}=\mathrm{V}_{\mathrm{D}}$ or $\frac{P}{Q}=\frac{R}{s}$. This is called condition of balance.### Balanced Wheatstone Bridge

The condition of balance depends on resistance P, Q, R and S. This is independent of emf of battery. In state of balance the cell and galvanometer can be interchanged. While performing an experiment at start press the cell key $K_{c}$ first and then the galvanometer key $\mathrm{K}_{9}$ and at end remove $\mathrm{K}_{9}$ first and then $\mathrm{K}_{\mathrm{c}}$ to avoid induced effects. P and Q are called ratio arms, R is known resistance arm and S is the unknown arm. BD and AC are called**conjugate arms.**

**The resistance of balanced wheatstone bridge between A and C is $\frac{(P+Q)(R+S)}{P+Q+R+S}$.**The sensitivity of bridge depends upon value of resistances. The sensitivity is maximum when P, Q, R and S are of same order.

#### Unbalanced Wheatstone bridge

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### Applications of Wheatstone Bridge

The**Wheatstone Bridge**has many uses in electronic circuits other than comparing an unknown resistance with a known resistance. When used with Operational Amplifiers, the Wheatstone bridge circuit can be used to measure and amplify small changes in resistance, R

_{X}due. Wheatstone bridge is not suitable for measurement of very small and very high resistances. Very low resistances are measured by

**Kelvin’s double bridge**while very high resistances by

**leakage method.**For Complete Study Material and Video Tutorials for JEE & NEET Exam Preparation

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**Also Read:**

- Types and Effects of Electric Current
- Ohm’s Law and Resistance
- Combination of Resistances
- EMF and Internal Resistances of a Cell
- Cells Connected in Series, parallel and Mixed
- Kirchhoff’s Circuit Law
- Electric Currents in Conductors
- Wheatstone Bridge
- Post office Box
- Wheatstone Meter Bridge
- Moving Coil galvanometer
- Ammeter and Voltmeter
- Potentiometer Working Principle