Wheatstone bridge, Construction, formula, derivation, principle, diagram & Application
Table of Contents
To investigate the world around them, scientists employ a variety of skills. They observe things and gather data using their senses. Simple observations include determining an object’s texture and color. However, if researchers want to learn more about a substance, they might need to conduct measurements. Measurement is a crucial component of science. Without the ability to measure, experiments cannot be performed and theories cannot be developed. Thus, Samuel Hunter Christie created the Wheatstone bridge in 1833 to measure unknown resistance in a circuit, which Sir Charles Wheatstone later popularized in 1843.
What is Wheatstone Bridge?
By balancing the two bridge circuit legs, the Wheatstone bridge, also referred to as the resistance bridge, determines the unknown resistance. There is an unidentified resistance component in one leg. So The Wheatstone Bridge Circuit consists of a bridge-shaped connection between two known resistors, one unknown resistor, and one variable resistor. This bridge is very trustworthy because it provides precise measurements.
Construction of Wheatstone Bridge
A Wheatstone bridge circuit has four arms, two of which are made up of known resistances and the other two of which are made up of unknown and variable resistance. An electromotive force source and galvanometer are also included in the circuit. The galvanometer is connected between points c and d, and the emf source is attached between points a and b. The potential difference of the galvanometer determines the current that flows through it.
What is the Wheatstone Bridge Principle?
The Wheatstone bridge operates on the null deflection theory, which states that no current flows through the circuit when the resistance ratios of the two components are equal. The bridge is normally out of balance, allowing current to flow through the galvanometer. When there is no current flowing through the galvanometer, the bridge is said to be balanced. By adjusting the known resistance and variable resistance, this condition can be achieved.
Wheatstone Bridge Derivation
As the current enters the galvanometer, it splits into two currents of equal magnitude, I1 and I2. When a galvanometer reads zero current, the following circumstance exists:
I1P=I2R……(1)
So The currents in the bridge, in a balanced condition, are expressed as follows:
I1=I3={E/(P+Q)}
I2=I4={E/(R+S)}
Here, E is the emf of the battery.
So By substituting the value of I1 and I2 in equation (1), we get
{PE/(P+Q)} = {RE/(R+S)}
{P/(P+Q)} = {R/(R+S)}
{R*(P+Q)} = {P*(R+S)}
PS = RQ……(2)
R =(P/Q)*S……(3)
So Equation (2) depicts the bridge’s balance, and equation (3) establishes the amount of the unknown resistance. So In the diagram, R stands for the unmeasured resistance, S for the bridge’s standard arm, and P and Q for its ratio arm.
Wheatstone Bridge Formula
For the Wheatstone Bridges, the following formula was used:
R =(P/Q)*S
Where,
- S is the standard arm of the bridge
- R is the unknown resistance
- P and Q is the ratio of the arm of the bridge
Application
- For the accurate measurement of low resistance, the Wheatstone bridges is employed.
- So Physical parameters like temperature, light, and strain are measured using a Wheatstone bridges and an operational amplifier.
- Variations of the Wheatstone bridge can be used to measure things like impedance, inductance, and capacitance.
Limitations
- The resistance of the leads and contacts becomes significant and introduces an error for low resistance measurements.
- The measurement provided by the bridge for high resistance measurements is so large that the galvanometer is insensitive to imbalance.
- So The resistance change brought on by the resistance being heated by the current is the other drawback. So Even a permanent change in the value of resistance could result from excessive current.