Conduction

Activity

3
Introduction

Conduction occurs when heat energy is transferred through a material without

the material itself moving. This happens due to the collision and interaction of particles
within the material, such as atoms or molecules, which pass kinetic energy along from
hotter regions to cooler ones. In this case, the atoms in the hotter regions have more
kinetic energy, on the average, than their cooler neighbors. They jostle their neighbors,
giving them some of their energy and this will continue and goes on. The atoms don’t
move from one region of material to another, but their energy does, whether its solid-
solid or solid-liquid.

Most metals conduct heat by another more effective mechanism. Within the
metal, some electrons can leave their parent atoms and wander through the metal.
These “free” electrons can rapidly carry energy from hotter to cooler regions of the metal,
so metals are generally good conductors of heat. A metal rod at 20°C feels colder than
a piece of wood at 20°C because heat can flow more easily from your hand into the
metal. The presence of “free” electrons also causes most metals to be good electrical
conductors.

Conduction also takes place in liquid-to-liquid interface. When two liquids with
different temperatures are in contact, heat is transferred across the interface through
conduction. Molecules in the hotter liquid have higher kinetic energy, and they collide
with the molecules in the cooler liquid, transferring energy directly at the boundary. The
rate of heat transfer depends on the thermal conductivity of the material and the
temperature gradient across the interface.

Heat flow is spontaneous but due to imperfections in the material (e.g. lattice
defects and impurities) and restrictions in atomic vibrations which impedes the transfer of
energy from one atom to another. This restriction adds up to the resistance of the
material. Materials with high heat resistance (𝑅𝐻𝑒𝑎𝑡 ∝ 1⁄𝑘) is called a heat insulator. The
mathematical foundation of heat conduction is described by Fourier’s Law of
Conduction, which states that the rate of heat transfer through a material is proportional
to the temperature gradient and the material’s thermal conductivity. Hence, given by
the equation,

𝑘𝐴(𝑇𝐻 − 𝑇𝐶 )
𝐻= ; (𝐻𝑒𝑎𝑡 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒)
𝐿

In this experiment, we investigate the principles of heat conduction by analyzing

the rate of heat transfer through a metallic rod. By visualizing the flow of heat, we aim to
observe how temperature distributes along the rod over time and how different factors,
such as material properties and boundary conditions, influence the conduction process.
Objectives

• To examine the principles of heat conduction using Fourier’s Law.

• To visualize the rate of heat distribution along the metal rod over time using wax
and thumbtacks.
• To investigate how different factors such as material type and temperature
gradient influence the conduction process.

Materials

o Metal Clamp
o Metal Stand
o Metallic rod
o Candle wax
o 4-5 pieces thumbtacks
o Alcohol lamp
o Timer
o Ruler
o Cold water

Methodology

1. Mark five (5) equidistant points along the metal rod. Melt candle wax on each
point and immediately attach a thumbtack before the wax hardens.
2. Use a ruler to measure and record the distances between the thumbtacks.
3. Secure the metal clamp to the metal stand, then attach the metal rod
horizontally so that the thumbtacks point downward.
4. Light the alcohol lamp and place it at one end of the metal rod.
5. Record the time at which each thumbtack falls. Repeat this process for four (4)
trials.
6. Immerse the opposite end of the metal rod in cold water, then repeat steps 4
and 5.
7. Plot the results using Excel or any plotting software.

Trial Thumbtacks 1 Thumbtacks 2 Thumbtacks 3

Thumbtacks
4
Thumbtacks
5
Dist = ____1.27cm Dist = ___1.27cm Dist = ___1.27cm Dist = Dist =
_______ _______
Before 1 00:00:12.01 00:00:31.49 00:01:51.98
immersing 2 00:00:32.51 00:02:13.06 00:07:44.88
in cold 3 00:02:12.54 00:25:24.28 00:11:26.81
water 4
After 1 00:00:35.30 00:01:23.47 00:01:55.20
immersing 2 00:01:43.24 00:03:23.08 00:09:32.05
in cold 3 00:03:44.36 00:28:19.01 00:31:28.48
water 4
Questions:

1 Explain operationally how does this experiment helps visualize the rate of heat
distribution along the metal rod?

This experiment uses melting wax and falling thumbtacks to show how heat travels. The
order and timing of the falling thumbtacks illustrate the pattern and speed of heat
distribution within the material.

2 How does the distance from the heat source affect the time it takes for wax to
melt at different points on the rod? What factors might cause discrepancies in
the observed melting times for thumbtacks?

Melting time increases with distance from the heat source because heat energy
spreads out, decreasing its intensity. Discrepancies in results can arise from inconsistent
wax thickness, variations in how the thumbtacks are attached, heat loss to the
surroundings, and uneven heating of the experimental apparatus.

3 What is the effect of immersing the opposite end of the metal rod in cold water
at the rate of heat transfer in this experiment? Explain the concept behind it.

Immersing the opposite end of the rod in cold water significantly slows heat transfer by
creating a large temperature gradient and acting as a heat sink, rapidly removing heat
from the system.

4 Why do metals generally have higher thermal conductivities compared to non-

metals?

Metals are better conductors of heat because of their free electrons, which transfer
thermal energy much more efficiently than the atomic vibrations (phonons) responsible
for heat transfer in non-metals. This difference in conduction mechanisms accounts for
the perceived coldness of metals compared to wood at the same temperature.

Summary

The experiment investigated heat conduction in a metallic rod, observing the time it
took for thumbtacks to fall off due to wax melting. Cooling the rod with water
significantly slowed this process. This observation supports Fourier’s Law, showing that
the rate of heat transfer is affected by both the material’s thermal properties and the
presence of a cooling agent. The cooling process initially increased heat loss but
ultimately resulted in a slower release of heat energy from the rod.
PLOT: