The metre bridge, also referred to as a slide wire bridge, is a device that operates based on the Wheatstone bridge principle. This apparatus is utilized to ascertain the unknown resistance of a conductor. This article will guide you through an experiment on how to measure the resistance of a given wire using a metre bridge and how to calculate the resistivity of its material.
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The aim of this experiment is to measure the resistance of a given wire using a metre bridge and to subsequently determine the resistivity, also known as specific resistance, of its material.
The metre bridge apparatus, also known as a slide wire bridge, is attached to a wooden block and consists of a long wire of uniform cross-sectional area. It features two gaps created with thick metal strips to form the Wheatstone’s bridge.
According to Wheatstone’s principle, we have:
The unknown resistance can be calculated as:
Then the specific resistance of the material of the wire is calculated as:
Where,
More Information: Wheatstone’s Bridge
Length of the given wire L =…….cm
Table for unknown resistance (X)
| Resistance from box, R (Ohm) | Length AB = l (cm) | Length BC = (100-l) (cm) | Unknown Resistance X = [R(100-l)]/L (Ohm) |
| 0.5 | 58.3 | 41.7 | 0.35 |
| 0.7 | 60.7 | 39.3 | 0.45 |
| 1 | 61.9 | 38.1 | 0.61 |
| 1.5 | 61.1 | 38.9 | 0.95 |
Least count of the screw gauge
Pitch of screw gauge = …….mm
Total no.of divisions on the circular scale = ………..
∴ L.C of the given screw gauge =
= ……mm
Zero error e = ……mm
Zero correction c = -e = ……mm
Radius of the resistance wire
| Main scale reading (mm) | Circular scale reading | Total reading (diameter) (mm) | Mean D (mm) | Mean radius (D/2) (mm) |
| 0 | 43 | 0.43 | 0.42 | 0.21 |
Calculation for X
Determine the value of l from the position of D and record it in column 3 of Table 1.
Find the length (100 – l) cm and write it in column 4.
Calculate X and write it in column 5,
Calculation for D
Mean corrected diameter =
Calculation for specific resistance
Specific resistance of the material of the given wire,
Standard value of the specific resistance of the material of the given wire,
ρ 0 = …..ohm.m
Percentage error =
= ………%
Q1. Why is it called a metre bridge?
Ans: It's named a metre bridge because the bridge uses a wire that's one meter long.
Q2. What is the null point?
Ans: The null point is the point at which the galvanometer shows zero deflection.
Q3. Why is the bridge method superior to Ohm's law for measuring resistance?
Ans: The bridge method is superior because it employs a null method.
Q4. What is the range of resistance that can be measured using a Wheatstone bridge?
Ans: The Wheatstone bridge can be used to measure resistance ranging from 1Ω to several megaohms.
Q5. How can a Wheatstone bridge be used to measure physical parameters?
Ans: A Wheatstone bridge can be used to measure physical parameters like temperature and light by using an operational amplifier. Rectifiers are used to convert AC to DC.
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Related Articles: |
Why is the metre bridge called so?
It is called a metre bridge because the bridges use one-meter long wire.
What is the null point?
Null point is defined as the point at which a galvanometer reads 0 deflections.
Why is the bridge method better than the Ohms law of measurement?
Bridge method is better than the Ohms law of measurement because of the null method.
What is the range of measurement of resistance using a Wheatstone bridge?
The resistance measurement range using a Wheatstone bridge is between 1Ω to a few megaohms.
How can a Wheatstone bridge be used for the measurement of physical parameters?
Wheatstone bridge is used to measure the physical parameters like temperature, light, etc, using an operational amplifier and rectifiers are used for the conversion of A.C to D.C.