Учебное пособие Казань-2016 Сайфуллина М. Н., Хабирова Н. М. English for Physicists



Pdf көрінісі
бет22/59
Дата08.11.2023
өлшемі1,1 Mb.
#190300
түріУчебное пособие
1   ...   18   19   20   21   22   23   24   25   ...   59
Байланысты:
Posobie dlya fizikov Habirova Sajfullina ispravv

Thermal Expansion 
When a material is heated or cooled, it changes its dimensions. 
Generally, it expands when heated and contracts when cooled although
there can be exceptions to this rule. 
Examples: If water is gradually cooled, it shrinks in size as expected. 
But at 3.98 ºC it begins to expand again until it turns to ice at 0 ºC. This 
expansion is peculiar to water and is associated with the unusual shape of 
the water molecule. This behavior explains why lakes freeze from the top 
downwards in winter. The colder water is at the top of the lake because it 
expands and becomes less dense. When this water freezes it insulates the 
water below it from the outside cold air like a blanket. It is because of this 
property many fish can survive the winter rather than becoming part of a 
giant Popsicle. 
When you first turn on a hot water tap, the water rushes out but is still 
cold. When it starts to become hot, the flow of water starts to become less 
and in some cases it stops. This can be explained as follows: the hot water 
heats the metal valve inside the tap which expands to block off any more 
flow of water. The change in length of a solid is related to the original 
length and the change in temperature. 
, where ∆ L is the change in length, L

is the original 
length before the change, ∆T is the change in temperature, and
is the 
linear thermal coefficient of expansion, which is different for different 
materials. 


44 
Thermal Expansion at the atomic level 
At the atomic level, thermal expansion means there is an increase in the 
average spacing between atoms. As a particular atom oscillates about its 
equilibrium position, it experiences an asymmetric potential energy as 
shown in figure 2. If it moves towards another atom it experiences a very 
steep rise in the potential energy. Whereas if it moves away from the other 
atom, it experiences a relatively slow increase in the potential energy and so 
travels much further. The asymmetry in the potential energy curve leads to a 
shift in the average position of the atom. 
(Adopted from 


Достарыңызбен бөлісу:
1   ...   18   19   20   21   22   23   24   25   ...   59




©engime.org 2024
әкімшілігінің қараңыз

    Басты бет