13 Jul 2026

Temperature Coefficient of Resistance of a Wire

practical ug-v thermal-physics resistance temperature-coefficient

Aim

To determine the temperature coefficient of resistance of the material of a wire.

Apparatus

Resistance wire, Wheatstone bridge, galvanometer, resistance box, water bath, thermometer, and battery.

Theory

For a conductor over a limited temperature interval,

\[R_t=R_0(1+\alpha t).\]

The slope of the $R$ versus $t$ graph gives $R_0\alpha$.

Observations

Temperature (°C)	Resistance (Ω)
20	5.42
40	5.84
60	6.25
80	6.67

Graph

Resistance-temperature graph for the experimental wire.

Extrapolated resistance at $0^\circ\text{C}$: $R_0=5.00\,\Omega$.

Calculation

Using the $20^\circ\text{C}$ reading,

\[\alpha=\frac{5.42-5.00}{5.00\times20}=4.20\times10^{-3}\, ^\circ\text{C}^{-1}.\]

Result

\[\boxed{\alpha=4.2\times10^{-3}\, ^\circ\text{C}^{-1}}.\]

Precautions

1. Maintain uniform bath temperature.
2. Use a small bridge current.
3. Avoid loose electrical contacts.
4. Take readings only after thermal equilibrium.

Viva Questions

1. Why does metallic resistance increase with temperature? Lattice vibrations increase scattering of conduction electrons.
2. Why is a bridge used? It permits accurate comparison of small resistance changes.
3. What is $R_0$? Resistance extrapolated to zero degree Celsius.

Maxima Code

Download the Maxima calculation file.