How to find Thermal conductivity of a bad conductor using Lee's disc method?

    In the second year of the B.Sc. Physics program under the TANSCHE curriculum, students dive into important thermal properties of materials by conducting different experiments. One interesting experiment involves measuring the thermal conductivity of a poor conductor using Lee's Disc Method. This hands-on activity helps students understand how heat moves through materials that don’t conduct heat well, giving them essential knowledge about thermal energy transfer in less effective conductors.

    In this article, we will explain the setup and steps involved in the Lee's Disc Method. This practical experience is vital for grasping thermal properties, preparing students for future scientific inquiries and practical applications in the real world.

Thermal conductivity of a bad conductor - 

Lee's disc method

Aim:

To determine the thermal conductivity of a bad conductor using Lee’s disc.

Apparatus required:

Lee’s disc, steam chamber, thermometers, bad conductor, screw gauge, vernier caliper, stop clock etc

Formula:

Here,

K is the thermal conductivity W/m/K

M is the mass of the Lee’s disc kg

s is the specific heat capacity of the Lee’s disc (370 J/kg/K)

d is the thickness of the bad conductor m

r is the radius of the Lee’s disc m

t is the thickness of the Lee’s disc m

is the steady temperature of the steam chamber oC

is the steady temperature of the Lee’s disc oC

Procedure:

   First, the mass (m) of the disc and the thickness (t) of Lee's disc are measured using a screw gauge. The thickness (d) of the bad conductor is also measured with the screw gauge. To find the diameter and radius (r) of the bad conductor, vernier calipers are used.

Next, steam is introduced into the steam chamber for a sufficient amount of time until the thermometers T1 and T2 show stable temperatures. The steady temperatures, for the steam chamber and for Lee's disc, are recorded. After that, the bad conductor is taken out. The Lee's disc is heated directly in contact with the steam chamber until its temperature increases by about 5ºC above the steady temperature .

Once this is done, the steam chamber is removed, and the Lee's disc is allowed to cool down. A stopwatch is started when the temperature is 5ºC above the steady temperature and time is noted for every 1ºC fall in temperature until the Lee’s disc attains 5ºC below .

Finally, a time-temperature graph is created. The time (t) in seconds that it takes for the Lee's disc to cool from ( + 1/2)°C to ( - 1/2)°C is noted from the graph. Then, the rate of cooling (d/dt) is calculated.

The steady temperature of steam chamber is = ____ oC

The steady temperature of Lee’s disc is = ____ oC

Tabular Column 1: To find time vs temperature

Time  s	Temperature oC

Tabular Column 2: To find the radius of the Lee's disc using Vernier calliper

            The procedure of using Vernier caliper and its table can be found here.

Tabular Column 3: To find the thickness of the Lee's disc using screw gauge

            The procedure of using Screw gauge and its table can be found here.

Tabular Column 3: To find the thickness of the bad conductor using screw gauge

            The procedure of using Screw gauge and its table can be found here.

Result: 

The thermal conductivity of the bad conductor using Lee’s disc method is found to be as, K = _____ W/m/K