Meter Bridge or Slide Wire Bridge is a practical form of Wheatstone bridge.

Wheatstone Bridge:
The Wheatstone bridge is a circuit used to measure unknown resistance by balancing it against a known resistance. It consists of four resistors arranged in a diamond shape, with a galvanometer connected between two opposite corners and a battery connected to the other two corners. When the bridge is balanced, the galvanometer shows zero deflection, indicating that the ratio of the unknown resistance to the known resistance is equal to the ratio of the other two resistors.

Meter Bridge or Slide Wire Bridge:
The meter bridge, also known as the slide wire bridge, is a practical form of the Wheatstone bridge. It consists of a long uniform wire of uniform cross-section called the meter wire, which is stretched over a wooden board. The meter wire is usually made of manganin or constantan, which have low temperature coefficients of resistance.

Construction:
The meter bridge consists of a uniform wire AB, which is connected to a galvanometer G at its midpoint. The wire is divided into two parts by a gap at the center, where a resistance box is connected. A jockey J is used to make contact with the wire and slide along its length.

Working Principle:
To measure an unknown resistance using the meter bridge, the jockey is initially placed at the midpoint of the wire (point O). The resistance box is adjusted until the galvanometer shows zero deflection. At this point, the bridge is in a balanced condition.

The principle behind the working of the meter bridge is that when the bridge is balanced, the ratio of the lengths of the two arms of the wire (AO and OB) is equal to the ratio of the resistances (R1 and R2) in the two arms. Mathematically, this can be represented as:

R1/R2 = AO/OB

By measuring the lengths AO and OB, the ratio R1/R2 can be determined. Since one of the resistances (R1 or R2) is known, the unknown resistance can be calculated.

Advantages of Meter Bridge:
1. High Accuracy: The meter bridge offers high accuracy in measuring resistance as it is based on the principle of a balanced bridge.
2. Simple Construction: The meter bridge is relatively simple in construction and easy to use.
3. Low Cost: The materials required for constructing a meter bridge are easily available and inexpensive.
4. Versatility: The meter bridge can be used to measure a wide range of resistances, making it a versatile instrument.

In conclusion, the meter bridge or slide wire bridge is a practical form of the Wheatstone bridge and is used to measure unknown resistances accurately.