In physics, the term "thermal expansion" refers to the expansion that takes place when heat is applied to a body. Each molecule in a body has an increased kinetic energy when it is heated. Molecular collisions between molecules happen more frequently as a result of the increase in kinetic energy. Now, when collisions happen, objects with greater kinetic energy than before will create a larger space around them. Practically, this results in growth.
Now, relating it to equation part:
Depending on the force of attraction acting between molecules, each substance has a specific arrangement and packaging. Therefore, the object with less attraction will occupy more space around it while using less kinetic energy than the object with more attraction. Therefore, for various metals, the coefficient of thermal expansion has been established experimentally.
for example: coefficient of thermal expansion of copper is 16.6∗10−6m/mK.
16.6∗10−6m/mK. That means if you apply 1 kelvin of heat on a copper rod of length 1 m, it will expand 16.6∗10−6 m more.
Expansion ∞ Length Lo (i) Note: ∞ is for proportionality sign.
Suppose an iron rod of 10 m and other of 1 m, obviously the larger one will expand more. (other functions remain same)
Expansion ∞ Change in Temperature - Δ (ii)
The more the temperature the higher kinetic energy the molecules posses. Therefore more expansion.
Therefore, on combining Expansion = α L0 ΔT Here α is the thermal expansion of the material.
Now adding L0 on both sides and taking L0 common on the right side (to get the new length of the rod)
L= L0(1+αΔT)
This is for linear expansion, similarly you can relate for superficial and cubical expansion.
The molecules slow down when solids cool. The solids shrink as a result of the molecules being able to move closer together. When heated, solids expand. Additionally, they undergo a process known as thermal contraction when they are cooled.
Thank you,
Eddie