A Brief Explanation

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The Wheatstone bridge is an electrical circuit used to precisely measure unknown resistances by balancing two legs of a bridge circuit. It was invented by Samuel Hunter Christie in 1833 and later popularized by Sir Charles Wheatstone in 1843.

 

Components of the Wheatstone Bridge

 

 

Four Resistors

(R1, R2, R3, R4) the circuit consists of four resistors arranged in a diamond Shape. The resistor R4 is typically the unknown resistor be measured.

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Voltage Source

(V): A voltage source is connected across the bridge, supplying power to the circuit.

 

Galvanometer

(G): A sensitive current-measuring device, like a galvanometer, is connected between the two midpoints of the bridge (the junctions of R1-R2 and R3-R4). This measures the current that flows through the bridge.

 

Configuration

R1 and R2 form one leg of the bridge.

R3 and R4 form the other leg.

 

Principle of Operation

The Wheatstone bridge works on the principle of null deflection, where the bridge is balanced, and no current flows through the galvanometer. This happens when the ratio of the resistances in one leg is equal to the ratio in the other leg:

R1R2=R3R4\frac{R1}{R2} = \frac{R3}{R4}R2R1​=R4R3​

When the bridge is balanced, the voltage at the two midpoints (where the galvanometer is connected) is the same, resulting in no current flowing through the galvanometer.

 

Calculation of Unknown Resistance

If the bridge is balanced, the unknown resistance R4R4R4 can be calculated using the known values of the other resistors:

R4=R3×R2R1R4 = \frac{R3 \times R2}{R1}R4=R1R3×R2​

 

Applications

Precise Measurement of Resistance

It is widely used in laboratories and industries for accurate measurement of unknown resistances.

 

Temperature Sensing

By replacing one resistor with a temperature-dependent resistor (thermistor or RTD), the Wheatstone bridge can be used as a temperature sensor.

 

Strain Gauges

In mechanical engineering, it is used to measure strain through strain gauges, where the strain gauge changes resistance under stress.

 

The Wheatstone bridge is valued for its accuracy and simplicity, making it a fundamental tool in electrical measurement.