What is Wheatstone Bridge? | Principle of Wheatstone Bridge | Derivation of Wheatstone Bridge | Application | Limitations |

What is Wheatstone Bridge?

A Wheatstone bridge is an electrical circuit used to measure the resistance of a component. It consists of four resistors arranged in a diamond shape, with a voltage source applied across the diagonal corners and a measuring device, such as a meter, connected across the other two corners. When the resistances of the four resistors are properly balanced, the current through the measuring device is zero, indicating that the resistance of the component being measured is equal to one of the resistors in the circuit. The Wheatstone bridge is commonly used in electrical and electronic applications to accurately measure resistance, often as part of a calibration process.

Principle of Wheatstone Bridge

The principle of the Wheatstone bridge is based on the relationship between voltage, current, and resistance in an electrical circuit. When a voltage is applied across a resistor, a current will flow through the resistor, and the magnitude of the current will depend on the resistance of the resistor and the voltage applied across it. The Wheatstone bridge uses this relationship to accurately measure the resistance of a component by applying a known voltage across the circuit and measuring the resulting current. The circuit is set up in such a way that the resistance of the component being measured is balanced against the resistances of the other three resistors in the circuit, allowing the resistance of the component to be calculated based on the known values of the other resistors.

Derivation of Wheatstone Bridge

The Wheatstone bridge circuit can be derived using basic principles of electrical circuits and Ohm's law, which states that the current through a resistor is directly proportional to the voltage applied across it. The basic Wheatstone bridge circuit consists of four resistors, R1, R2, R3, and Rx, arranged in a diamond shape, as shown below:

The derivation of the Wheatstone Bridge involves analyzing the current flow through the circuit to determine the relationship between the known resistances and the unknown resistance. The current through the galvanometer at the balanced condition of the bridge is zero, which is IG = 0. The current through arms AB and BC is denoted by I1, while the current through arms of AD as well as DC is I2. As per the circuital law of Kirchhoff, voltage drop through the closed-loop is 0 .

To create a Wheatstone Bridge condition, no current should pass through wire CD, or the potential at point C and D must be the same. In the circuit diagram, R1 and R2 are known resistors, R3 is a variable resistor, and R4 is the unknown resistance.

In conclusion, the Wheatstone Bridge circuit is an important tool for measuring unknown resistances. Its derivation involves analyzing the current flow through the circuit, and the balanced condition is achieved when no current flows through the middle arm of the circuit. Samuel Hunter Christie and Sir Charles Wheatstone invented and improved the Wheatstone Bridge in the early 1800s, and it was initially used for soil analysis and comparison.

Application of Wheatstone Bridge

The Wheatstone bridge is a widely used circuit in electrical and electronic applications for accurately measuring resistance. Some common applications of the Wheatstone bridge include:

• Calibrating instruments: The Wheatstone bridge can be used to calibrate instruments that measure resistance, such as ohmmeters, multimeters, and resistance bridges.
• Measuring temperature: The Wheatstone bridge can be used to measure temperature by using a temperature-dependent resistor, such as a thermistor, as the component being measured. The resistance of the thermistor will change with temperature, and the Wheatstone bridge can be used to accurately measure this change and convert it to a temperature reading.
• Measuring strain: The Wheatstone bridge can be used to measure strain in a material by using a strain gauge as the component being measured. A strain gauge is a device that changes resistance in response to strain, and the Wheatstone bridge can be used to accurately measure this change and convert it to a strain reading.
• Measuring pressure: The Wheatstone bridge can be used to measure pressure by using a pressure sensor as the component being measured. A pressure sensor is a device that changes resistance in response to pressure, and the Wheatstone bridge can be used to accurately measure this change and convert it to a pressure reading.

Limitations of Wheatstone Bridge

Although the Wheatstone bridge is a powerful and widely used circuit for measuring resistance, it has some limitations that should be considered when using it. Some of the main limitations of the Wheatstone bridge include:

• Sensitivity: The Wheatstone bridge is not as sensitive as some other methods of resistance measurement, such as the Kelvin bridge, which can measure resistance with greater precision and accuracy.
• Temperature: The Wheatstone bridge is sensitive to temperature, and the resistance of the resistors in the circuit may change with temperature, affecting the accuracy of the measurement. To compensate for this, the Wheatstone bridge must be calibrated at a known temperature, or temperature compensation must be applied.
• Frequency: The Wheatstone bridge is designed to measure DC resistance, and its accuracy may be affected when measuring AC resistance at high frequencies.
• Reference resistors: The Wheatstone bridge relies on the use of accurate reference resistors, which must be carefully selected and matched to ensure the accuracy of the measurement.

Overall, the Wheatstone bridge is a useful and powerful circuit for measuring resistance, but it has some limitations that should be considered when using it.

Frequently asked questions 

⇒ What is a Wheatstone bridge?

A Wheatstone bridge is an electrical circuit used to measure an unknown resistance by comparing it to a known resistance.

⇒ Who invented the Wheatstone bridge?

The Wheatstone bridge was invented by Samuel Hunter Christie in 1833, but it was named after Sir Charles Wheatstone, who popularized its use.

⇒ What are the components of a Wheatstone bridge?

A Wheatstone bridge consists of four resistors arranged in a diamond shape with an unknown resistance in one arm of the diamond.

⇒ What is the principle of a Wheatstone bridge?

The principle of a Wheatstone bridge is based on the fact that the voltage across two points in a circuit is proportional to the resistance between those points.

⇒ What is the equation for a Wheatstone bridge?

The equation for a Wheatstone bridge is R1/R2 = R3/R4, where R1 and R2 are the two resistors of known values, and R3 is the unknown resistance being measured.

⇒ What is the balance point of a Wheatstone bridge?

The balance point of a Wheatstone bridge is the point at which the voltage across the bridge is zero, indicating that the unknown resistance has been accurately measured.

⇒ What is the sensitivity of a Wheatstone bridge?

The sensitivity of a Wheatstone bridge is the ratio of the change in output voltage to the change in the measured quantity.

⇒ What are some applications of Wheatstone bridges?

Wheatstone bridges are used in many applications, including strain gauges, temperature sensors, and pressure sensors.

⇒ What are the advantages of using a Wheatstone bridge?

The advantages of using a Wheatstone bridge include high accuracy, low sensitivity to changes in voltage or temperature, and the ability to measure very small changes in resistance.

⇒ What are the limitations of a Wheatstone bridge?

The limitations of a Wheatstone bridge include the need for precise resistor values, the possibility of measurement errors due to temperature changes, and the fact that the bridge can only measure resistances within a certain range.

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