Null Detector in Wheatstone Bridge

The Wheatstone bridge is an electrical circuit that is used to measure an unknown resistance by balancing two legs of the circuit. The Wheatstone bridge consists of four resistors, with two of them known and the other two unknown. The circuit is balanced when the voltage difference between two points in the circuit is zero. The instrument used to detect this zero voltage difference is called the null detector.

Galvanometer as Null Detector

The galvanometer is used as the null detector in the Wheatstone bridge. A galvanometer is an instrument that measures small electrical currents. It works on the principle of electromagnetic induction. When a current flows through a wire, it creates a magnetic field around the wire. This magnetic field interacts with a permanent magnet inside the galvanometer and causes the needle to move.

The galvanometer is used as the null detector in the Wheatstone bridge because it is very sensitive to small changes in current. When the bridge is balanced, there is no current flowing through the galvanometer, and the needle remains at zero. When the bridge is unbalanced, a small current flows through the galvanometer, causing the needle to move. By adjusting the known resistors in the circuit, the bridge can be balanced, and the unknown resistance can be calculated.

Conclusion

In conclusion, the galvanometer is used as the null detector in the Wheatstone bridge because it is very sensitive to small changes in current. When the bridge is balanced, there is no current flowing through the galvanometer, and the needle remains at zero. When the bridge is unbalanced, a small current flows through the galvanometer, causing the needle to move. By adjusting the known resistors in the circuit, the bridge can be balanced, and the unknown resistance can be calculated.