Resistivity of a wire (metre bridge)

A/L Physics · G.C.E. Advanced Level · Grades 12–13

Aim

To find the resistance and resistivity of a wire using a metre bridge.

Apparatus

• Metre bridge and galvanometer
• Resistance box (R)
• Unknown wire (d = 0.30 mm, L = 1.00 m)

Method

1. Set a value of R on the resistance box.
2. Slide the jockey to the balance length l (zero deflection).
3. Calculate X = R(100 − l) ÷ l.
4. Repeat for several R, take the mean; then ρ = Xπd² ÷ 4L.

Conclusion

At balance R ÷ X = l ÷ (100 − l). The resistivity ρ is a property of the material.