Describe experiments to demonstrate the properties of good thermal conductors and bad thermal conductors (thermal insulators)

2.3.1 Conduction

Learning Objective

Describe experiments that demonstrate the properties of good thermal conductors and poor thermal conductors (thermal insulators).

Key Concepts

• Thermal conduction is the transfer of heat through a material without the material itself moving.
• Good conductors have high thermal conductivity (\$k\$) and allow heat to flow quickly.
• Insulators have low \$k\$ and restrict heat flow.

Experiment 1 – Identifying a Good Thermal Conductor

1. Apparatus

   • Metal rod (e.g., copper or aluminium) – length 30 cm, diameter 1 cm
   • Heat source – Bunsen burner or hot water bath
   • Thermometers (2) or temperature probes
   • Insulating stand
   • Stopwatch

2. Method

   1. Place the metal rod horizontally on the insulating stand.
   2. Attach one thermometer at the lower end (point A) and the second at the opposite end (point B).
   3. Heat point A by placing the flame of the Bunsen burner against it for 30 s.
   4. Record the temperature at point B every 10 s for 2 min.
   5. Repeat the experiment with the rod turned upside‑down to check repeatability.

3. Observations

   • Temperature at point B rises rapidly, reaching near the temperature of point A within a minute.
   • Temperature change is almost linear with time after the initial lag.

4. Conclusion

   The metal rod conducts heat efficiently, demonstrating that metals are good thermal conductors.

5. Safety Notes

   • Handle the hot rod with tongs or heat‑resistant gloves.
   • Keep the flame away from flammable materials.

Experiment 2 – Identifying a Poor Thermal Conductor (Insulator)

1. Apparatus

   • Wooden block (or Styrofoam) – same dimensions as metal rod
   • Heat source – hot water bath (≈80 °C)
   • Two thermometers or temperature probes
   • Insulating stand
   • Stopwatch

2. Method

   1. Place the wooden block on the stand and immerse one end in the hot water bath (point C).
   2. Place the second thermometer at the opposite end (point D).
   3. Record the temperature at point D every 30 s for 5 min.
   4. Compare the temperature rise with that recorded for the metal rod.

3. Observations

   • Temperature at point D increases very slowly; after 5 min it is only a few degrees above ambient.
   • Heat does not travel efficiently through the block.

4. Conclusion

   The wooden block (or Styrofoam) acts as a thermal insulator, confirming that non‑metallic, porous materials have low thermal conductivity.

5. Safety Notes

   • Avoid splashing hot water.
   • Do not place the block directly on a flame.

Comparative Data

Explanation Using the Heat Conduction Equation

The rate of heat transfer \$Q\$ through a material of cross‑sectional area \$A\$, thickness \$L\$, and temperature difference \$\Delta T\$ is given by

\$\$

Q = \frac{kA\Delta T}{L}

\$\$

For a good conductor, \$k\$ is large, so \$Q\$ is high for a given \$\Delta T\$ and \$L\$. For an insulator, \$k\$ is very small, making \$Q\$ negligible.

Extension Activities

• Investigate the effect of thickness \$L\$ on the rate of heat transfer by using rods of different lengths.
• Measure the thermal conductivity of an unknown material using the same set‑up and rearranging the equation for \$k\$.
• Design a simple thermos flask using layers of insulating material and test its performance.