Question

Lee's method for Bad conductor prove equations ​

Answer 1

Explanation:Measurement of Thermal Conductivity by Lee’s method

Aim:

To determine thermal conductivity of a bad conductor (glass) in form of a disc using

Lee’s method.

Requisites:

(1) Lee’s apparatus and the experimental specimen in the form of a disc.

(2) Two thermometers, (3) Stop watch, (4) Weighing balance, (5) Special lamp stand

(6) Boiler and (7) Heater

Theory:

Thermal conductivity, k, is the property of a material that indicates its ability to conduct

heat. Conduction will take place if there exists a temperature gradient in a solid (or stationary

fluid) medium. Energy is transferred from more energetic to less energetic molecules when

neighboring molecules collide. Conductive heat flow occurs in direction of the decreasing

temperature because higher temperature is associated with higher molecular energy. Fourier’s

Law expresses conductive heat transfer as

ܪ ൌ ݇ܣ ሺ்మି்భሻ

௫ (1)

where H is the steady state rate of heat

transfer, k is the thermal conductivity of

the sample, A is the cross sectional area

and (T 2 – T1) is the temperature difference

across the sample thickness ‘x’ (see Fig.

1), assuming that the heat loss from the

sides of the sample is negligible. To keep

the loss from the sides small, the sample is

made in form of a thin disk with a large

cross sectional area compared to the area

exposed at the edge. Keeping ‘A’ large and

‘x’ small produces a large rate of energy

transfer across the sample. Keeping x small

also means that the apparatus reaches a

steady state(when temperature T1 and T2 are constant) more quickly.

Generally speaking, there are a number of possibilities to measure thermal conductivity, each of

them being suitable for a limited range of materials, depending on the thermal properties and the

medium temperature. The most commonly used methods are Searle’s method and Lee’s disc

method, for good and bad conductors of heat, respectively. In the experiment, we will use Lee’s

disc method to determine the thermal conductivity of a bad conductor, e.g. Glass.