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



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Posobie dlya fizikov Habirova Sajfullina ispravv

READING 
Read and translate the text using a dictionary if necessary: 
Heat transfer is the transfer of thermal energy from a higher 
temperature object or system to another system, raising its temperature.
This process changes the thermal energy of both systems involved until 
thermal equilibrium is reached. Thermal energy can be transferred from one 
end of a material to the other or from one material to another through 
conduction. It is also transferred indirectly by convection and radiation. 
Conduction 
Thermal energy can be transferred from one substance to another when 
they are in direct contact. The moving molecules of one material can 
increase the energy of the molecules of the other. Heat can also travel along 
a material as one molecule transfers energy to a neighboring one. 
Conduction is mainly seen with solid objects, but it can happen when any 
materials come into contact. When you put your hand in a container of
warm water, you hand it heated by conduction from the water. 
Some materials are better conductors of heat than others. For example, 
metals are good conductors of heat, while a material like wood is not. Metal 
heated on one end will soon be hot on the other end too, while that is not 
true with a piece of wood. Good conductors of electricity are often good 
conductors of heat. Since the atoms are closer together, solids conduct heat 
better than liquids or gazes. This means that two solid materials in contact 
would transfer heat from one to the other better than a solid in contact with 
a gas or a gas with a liquid. 
Convection 
When a gas or a liquid is heated, hot areas of the material flow and mix 
with the cool areas. Forced air heating and air conditioning are examples of 
heating (or cooling) by convection. This is an effective way of bringing a 
hot (or cold) fluid to a different area. Convection transfers heat over a 
distance faster than conduction. But ultimately conduction must transfer the 
heat from the gas to the other object, though molecular contact. 
Radiation 
A third method to transfer heat is by radiation. A warm or hot object 
gives off infrared electromagnetic radiation, which can be absorbed in 


49 
another object at some separation, heating it up. However, the heat transfer 
only works in one direction. You cannot cool an object by radiation, as you 
can with conduction or convection. Electric heaters use radiation to heat an 
area. If a fan is added, the device uses both radiation and convection to heat 
the area. Transfer of heat by radiation travels at the speed of light and goes 
great distances, even in a vacuum. We are heated from the Sun through 
radiation transfer of heat. 
To summarize, thermal (heat) energy can be transferred from one 
substance to another or one end of a material to the other through 
conduction. Also it can be transferred indirectly by convection and
radiation. Atoms or molecules transfer kinetic energy to their neighbors 
through collisions. When objects are in contact this transfers heat by 
conduction. Liquids and gases can move high or low energy molecules to 
another region through convection. Atoms can radiate energy that can 
energize a distant atom, resulting in heat transfer by radiation. 
(Adopted from 
www.school-for-champions.com

 
 


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