Wheatstone Bridge

Wheatstone bridge is the bridge of networks used to find out the resistance of the circuit. Wheatstone bridge experiment was first conducted by Samuel Hunter Christie in the year 1833. It is widely used for calculating the unknown resistance in an electrical circuit.

Principle of Wheatstone bridge experiment

The principle of wheatstone bridge is based on the ‘Kirchoff’s law’. We basically have four resistances in our wheatstone bridge experiment. So, if we know the values of three resistances then we can easily calculate the value of the unknown resistance by putting it in the wheatstone bridge.

Wheatstone Bridge circuit
Wheatstone Bridge circuit

Components of Wheatstone bridge experiment

  • Four resistors (which are usually connected in the shape of diamond as shown)
  • Supply source (battery)
  • Galvanometer
  • Connecting Wires
  • Ammeter

In this, one resistor should always be variable to maintain a balanced condition and avoid the condition of unbalanced wheatstone bridge. The Circuit performs at its best when the regulated voltage source is used, instead of the current with repel characteristics,

It is basically used for finding the unknown resistance by putting it in an equation with known values and then comparing it. Balanced or null condition is necessary to find this unknown resistance through the wheatstone bridge.

Working of Wheatstone bridge

  • The circuit contains
  1. Two known resistors
  2. One variable resistor
  3. And, one unknown resistor
  • All these resistors are connected in the form of bridge.
  • When you adjust the variable resistor, then the reading in the galvanometer turns to zero.
  • And, we know that the ratio of two known resistors is equal to the ratio of value of unknown resistor and the variable resistor; according to the Kirchoff’s law.
  • Now, through this equation the value of the unknown one can be easily calculated.

The unknown value of the resistor in the circuit is also referred to as the wheatstone bridge sensor.

Examples of Wheatstone bridge

This network of bridges is usually used for the strain measurement in the electrical circuits.

For measuring the strain usually the strain gages are used. The electrical resistance of the strain gages varies with the increase or decrease in the strain of the device. The range of strain gage used in this application is from 30 ohms to 3000 ohms.

So, in measuring starin wheatstone bridge experiment is used for measuring the fraction of changes in resistance with high accuracy. Basically for strain measurement it is used; so that the measurement of strain can be calculated or measured more precisely and accurately.

Wheatstone bridges are also used in the thermometers for the temperature measurements which need to be accurate.

Role of Wheatstone bridge in Light Detectors

For light detection through wheatstone bridge, the type of resistors which should be used must be resistive sensors like potentiometers, thermistors and photoresistive sensors (LDR).

LDR is also referred to as cadmium-sulphide photocell. It is a resistive sensor which basically converts the changes that occur in light levels (visible light) into changes in resistance; that is basically into voltage.

Applications of Wheatstone bridge

  • It is used in the light detectors.
  • For measuring the changes in the intensity of the light.
  • For measuring the changes in the pressure.
  • For measuring the changes in the strain of the circuit.
  • They are also used for sensing mechanical and electrical quantities.
  • These circuits can also be used in devices like photoresistive devices.



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