13 Jul 2026

Temperature Coefficient of Resistance by Platinum Resistance Thermometer

practical ug-v thermal-physics resistance-thermometer platinum

Experimental arrangement

The platinum element is placed in the temperature bath and its resistance is measured at each steady temperature.

Aim

To determine the temperature coefficient of resistance of platinum using a platinum resistance thermometer.

Apparatus

Platinum resistance coil, bridge circuit, galvanometer, resistance box, thermometer, water bath, and heater.

Theory

For a moderate temperature range,

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

where $R_0$ is the resistance at $0^\circ\text{C}$ and $\alpha$ is the temperature coefficient. Thus,

\[\alpha=\frac{R_t-R_0}{R_0t}.\]

Observations

Resistance at $0^\circ\text{C}$: $R_0=10.00\,\Omega$.

Temperature (°C)	Resistance (Ω)	Calculated $\alpha$ (°C$^{-1}$)
20	10.78	0.00390
40	11.57	0.00393
60	12.36	0.00393
80	13.14	0.00393

Result

The temperature coefficient of platinum resistance is

\[\boxed{\alpha=3.92\times10^{-3}\, ^\circ\text{C}^{-1}}.\]

Precautions

1. Stir the water bath to maintain uniform temperature.
2. Wait for thermal equilibrium before measuring resistance.
3. Use small bridge current to avoid self-heating.
4. Record temperature and resistance simultaneously.

Viva Questions

1. Why is platinum used? It is stable, reproducible, and has a nearly linear resistance-temperature relation.
2. What is self-heating? It is the rise in thermometer temperature due to measuring current.
3. Why is a water bath used? It gives a uniform and controllable temperature.
4. How does resistance of platinum vary with temperature? It increases approximately linearly over a moderate range.

Maxima Code

Download the Maxima calculation file.