Resistance (R) 5Ω

1Ω 20Ω

Unknown Wire (X)

?

Material: Nichrome

Length: 50cm (Fixed)

SENSITIVE GALVANOMETER

0102030405060708090100

cm

Balancing Length (l)

0.0 cm

Remaining (100-l)

100.0 cm

Experimental Physics

Metre Bridge Experiment

Application of Wheatstone Bridge principle to find unknown resistance.

The Metre Bridge (or Slide Wire Bridge) is an instrument used to find the unknown resistance of a coil or wire. It works on the principle of the Wheatstone Bridge.

[Image of meter bridge circuit diagram]

Working Formula

At the null point (zero deflection in galvanometer), the ratio of resistances is:

$$ \frac{P}{Q} = \frac{R}{X} $$ → $$ X = R \left( \frac{100 - l}{l} \right) $$

Where:

R: Resistance from Resistance Box (Known)
X: Unknown Resistance
l: Balancing length (cm)
100-l: Remaining length (cm)

Viva Voce

Q: Why is it called a Metre Bridge?

Because it uses a resistance wire exactly one metre (100 cm) long stretched on a wooden board.

Q: Why do we use thick copper strips?

To minimize the resistance of the connecting leads. Thick strips have negligible resistance compared to the wire.

Q: What is End Error?

Error arising when the zero mark of the scale doesn't coincide exactly with the start of the wire, or due to contact resistance at the ends.

Lab Notebook

Trial #	Resistance Box (R)	Balancing Length (l)	100 - l	Unknown (X)
No readings recorded yet. Perform the experiment in the Simulation tab.

Calculated Mean Resistance

Average of all trials

-- Ω

Ad Space