What Is a Metre Bridge?

A metre bridge is a device that functions on the Wheatstone bridge idea. It is used to determine the unknown resistance of a substance, usually a conductor. In order to understand how a metre bridge functions, it is essential to first go through the basic concept of electric flow and the SI unit of electric flow. Here are some points to keep in mind:

• An electric flow is a flood of charged particles that travel through an electrical space. These moving particles are known as charge transporters. In the case of electric circuits, these charge transporters are regularly electrons travelling through a wire.
• The SI Unit of electric flow is the amp, or ampere, which measures the progression of electric charge across a surface at one coulomb per second. The ampere is used as the SI base unit of electric flow, which can be found using a device known as an ammeter.
• Now, we already know that electric flows make attraction fields possible, which are frequently used in generators, engines, transformers, and inductors.

A metre bridge, then, can be defined as an electrical device used to measure the value of unknown resistance. A metre bridge is made using a metre-long wire having uniform cross-sections. This wire is either made of nichrome, manganin, or constantan because they have high resistance and a low-temperature coefficient of resistance.

The metre bridge is called so because it is made up of a constantan/manganin wire that is exactly one metre long and has a uniform cross-sectional area across the entire one metre.

How Does a Metre Bridge Work?

A metre bridge works on the same principle as the Wheatstone bridge, named after the scientist who invented the concept, Sir Charles Wheatstone. It is frequently used in laboratories to determine the resistance of a metal coil or any other substance.

The basic metre bridge principle states that if at any point of the wire, the ratio of two resistances is equal to the ratio of another set of two resistances, then there will be no flow of current between those points and the edges that contain the resistances. The galvanometer will indicate that there is zero deflection at any point.

A Wheatstone connection is dependent on the rule of invalid avoidance. At the point where the proportion of protection of the two arms is equal, there will be no current moving through the centre arm of the circuit.

What do you need to find the unknown resistance using a metre bridge?

The devices that you require in finding the unknown resistance of any conductor with the use of a metre bridge include:

• Metre Bridge
• Resistance box
• Galvanometer
• Connecting wires
• Leclanche cell
• Jockey
• One way key
• Unknown resistance of a length of one metre
• Screw gauge

In the metre bridge, one of the lateral resistances can be replaced by a wire with a length of one metre and a uniform cross-section. The other pair of lateral resistance comprises one known and one unknown pair of resistances. One part of the galvanometer is connected in between two resistances, forming a bridge. In contrast, the other part of the wire is used for finding the null or zero point where the galvanometer does not show any deflection or the point of zero current. At this point, the metre bridge is said to be balanced.

How to Setup a Metre Bridge

Ensure that you have the materials mentioned above to build the metre bridge. Here are the steps to follow to set up a metre bridge.

1. Connect one end of the connecting wire to one point of the metre bridge and the other point to the positive terminal of the Leclanche cell.
2. Take another connecting wire and connect one end of the one-way key and the other end to the negative terminal of the Leclanche cell.
3. Take a third connecting wire and connect one end to any point on the metre bridge and the other end to the key.
4. Connect the variable resistance to both ends of the metre bridge and do the same with the unknown resistance wire.
5. Connect the central terminal of the metre bridge to the galvanometer’s positive terminal and connect the galvanometer’s negative terminal to the jockey.

You have successfully set up your metre bridge.

Are there any drawbacks to the metre bridge?

The metre bridge can be used to determine the resistance of a metal wire. However, it is not suitable to use for measuring high or low resistances as the bridge has maximum sensitivity. At the same time, a metre bridge wire might not precisely measure at one metre, which may cause a measurement error.

Conclusion 

A metre bridge is a device used to find out the unknown resistance of a conducting substance. An electric flow is a flood of charged particles, and it makes attraction fields possible. A metre bridge measures the value of unknown resistance and is made with a metre-long wire of uniform cross-section. The metre bridge works on the same principle as the Wheatstone Bridge, named after Sir Charles Wheatstone. Knowing how to set it up is important to understand its functioning.