Tanta university Faculty of science Physics department

Thermal Expansion

Applications Experiment Introduction

Introduction Thermal expansion is the tendency of matter to change in shape, area, and volume in response to a change in temperature , through heat transfer. Thermal expansion coefficient used to determine the rate at which material expands as a function of temperature.

Question(1): What is the reason for thermal expansion?

Types Of Thermal Expansion 3-Volume 2- Areal 1- Linear

Linear Expansion Linear expansion means change in one dimension (length) . "linear expansion coefficient". It is the fractional change in length per degree of temperature change. α=(1/L).(∆L/∆T) Young's modulus=stress/strain .

Areal Expansion The area thermal expansion coefficient relates the change in a material's area dimensions to a change in temperature It is the fractional change in area per degree of temperature change.

Volume Expansion The volume thermal expansion coefficient relates the change in a material's volume dimensions to a change in temperature It is the fractional change in volume per degree of temperature change.

Question (2): What is the difference between expansion in solids , liquids and gases?

Thermal Expansion Examples:

The Rail Ways :

Solutions:

Example (2)

Example (3)

negative thermal expansion. Thermal contract: negative thermal expansion.

When can we see the real shape of material? Question(3): When can we see the real shape of material?

Aim Of Experiment: Determining the expansion coefficient of a metallic rod.

Theory: Most bodies expands as their temperature increase. The overall thermal expansion consequence. The expansion for all atoms and molecules. Linear expansion is only for one dimension. The length increasing by amount ∆L as the temperature increases for ∆T. The change in length is proportional to change in temperature.

α=(1/L).(∆L/T) ∆L=α.L. ∆T Unit of expansion coefficient is (degree) -1 The basic equation for expansion of solids is: ∆L=α.L. ∆T Where α :is thermal expansion coefficient And then: Unit of expansion coefficient is (degree) α=(1/L).(∆L/T) -1

Experiment requirements:

Apparatus Of Experiment: Metallic micrometer. Metallic rod. Steam generator. Hot plate . Thermometer.

Method: Measure the length of the rod (L). Adjust the micrometer at zero. Fill the steam generator with water. Start heating. Rise the rod temperature till (95) degree. Record reducing in length against temperature. Plot a relation between change in length(∆L) and temperature (T).

THE GRAPH: -3 ∆L*10 Slope=α.∆L ∆T

Applications: 1-Thermometers:

2-Elecrical power lines:

We use hot water to remove Jar 3-Jar lids: We use hot water to remove Jar

4-roads and bridges:

Our results: Lo=55.5 (cm) To=23 (c) T (C) ∆T=T-To 80 80-23=57 61 75 -3 T (C) ∆T=T-To ∆L=L-Lo ×10 80 80-23=57 61 75 75-23=52 53 70 70-23=47 46 65 65-23=42 39 60 60-23=37 33 55 55-23=32 28

α=5.4×10 (c) -5 -1