Metre bridge
Learn the construction, working, and applications of the metre bridge as a practical form of the Wheatstone bridge.
What is Metre bridge?
The position of the jockey on the metre bridge wire where the galvanometer shows no deflection, indicating that the potential difference across the galvanometer is zero.
Key formula / rule: Metre Bridge Formula
Key points
- To understand the construction and working of a metre bridge.
- To apply the Wheatstone bridge principle to measure unknown resistance.
- To identify factors affecting the accuracy of the metre bridge experiment.
- To calculate unknown resistance using the metre bridge formula.
Common exam trap
Assuming the wire is perfectly uniform when it is not.
Definitions
- Term
Null Point
- Meaning
The position of the jockey on the metre bridge wire where the galvanometer shows no deflection, indicating that the potential difference across the galvanometer is zero.
- Term
Wheatstone Bridge
- Meaning
An electrical circuit used to measure an unknown resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.
- Term
Uniform Wire
- Meaning
A wire having constant cross-sectional area and uniform resistivity along its entire length, crucial for the metre bridge to work accurately.
Learning objectives
To understand the construction and working of a metre bridge.
To apply the Wheatstone bridge principle to measure unknown resistance.
To identify factors affecting the accuracy of the metre bridge experiment.
To calculate unknown resistance using the metre bridge formula.
Formulae
- Name
Metre Bridge Formula
- Note
Where X is the unknown resistance, R is the known resistance (from resistance box), l is the length of the wire from the zero end to the null point in cm, and (100-l) is the remaining length of the wire.
- Expression
X/R = l/(100-l)
- Name
Resistance per unit length
- Note
This is implicitly used, assuming uniform wire. The ratio of resistances is equal to the ratio of lengths.
- Expression
ρ = Resistance / Length
Prerequisites
Understanding of Ohm's Law
Concept of Electrical Resistance
Principle of Wheatstone Bridge
Series and Parallel Combinations of Resistors
Galvanometer as a current detector
Common mistakes
Assuming the wire is perfectly uniform when it is not.
Not ensuring good electrical contact between the jockey and the wire.
Reading the lengths incorrectly from the meter scale.
Using a galvanometer that is not sensitive enough to detect the null point.
Placing the unknown resistance and the resistance box in the wrong gaps.
Keywords
Metre Bridge
Wheatstone Bridge
Unknown Resistance
Null Point
Jockey
Galvanometer
Uniform Wire
Resistance Box
Slide Wire Bridge
Practice preview
What is the fundamental principle on which a metre bridge operates?…
easy
The wire used in a metre bridge is typically made of which material?…
easy
What is the primary application of a metre bridge?…
easy