Thermodynamics is the branch of physics that studies the relationships between heat, work, temperature, and energy. It explores how these concepts govern the behavior of matter in various states—solid, liquid, and gas. Understanding thermodynamics is essential for explaining phenomena such as the...
Thermodynamics is the study of temperature, heat, and exchange of energy. It has practical
applications in all branches of science and engineering including weather forecasting.
Temperature is a general term which refers to the hotness or coldness of an object. The
quantity of thermal energy in a material impacts its temperature. The same quantity of
thermal energy present in different bodies, however, does not each give the same quantity of
temperature. The ratio between temperature and thermal energy is different for different
materials. Temperature is also a physical property that determines the direction in which heat
energy will flow between substances. Temperature and heat do not mean the same,
temperature is a physical quantity with SI unit Kelvin and heat is a form of energy with SI unit
Joule.
Thermal Energy is the total potential and kinetic energy associated with the random motion
and arrangements of the particles of a material.
Heat is thermal energy that is absorbed, given up, or transferred from one body to another
.There is no instrument available that can directly measure the amount of thermal energy a
body gives off or absorbs. Therefore quantities of heat must be measured by the effects they
show. The temperature of a body measures its ability to give up or absorb heat from another
body. Heat flows from a body with a higher temperature to a body with lower temperature even
if the cooler body contains more thermal energy. The experiments of Count Rumford and
James Prescott Joule show that mechanical energy and heat are equivalent and heat must be a
form of energy.
Matter is made up of moving particles such as atoms, molecules, or ions. In the case of solids
these particles are tightly bonded together and so they will vibrate by keeping their equilibrium
position, whereas in fluids (liquid and gasses) , the particles can freely move around. Generally,
particles in all states have kinetic energy because of their motion and potential energy and the
attraction force between them.
The amount of energy transferred from one body to another by virtue of temperature
difference is called heat. When heat is added to body, one of the two things could happen
* The particles of the body gain more kinetic energy and move more rapidly. This is usually
resulted in increase in volume and temperature
, * The bonds between the particles in the substance are broken down. In this case, the
substance changes its state and thus the change in potential energy results.
Relationship Between Heat and Temperature
Assume that we fill a large and a small beaker with boiling water. The water in the two
beakers is at the same level of temperature, but the water in the large beaker give off more
heat. It could for instance melt more ice than could the water in the small beaker. It is therefore
logical to conclude that it is possible for a body to be at high temperature and give off little heat
and ; or to be at a low temperature and give off large quantity of heat. For example, the
temperature of the air in a bicycle tire will rise when it is being pumped up. It will also rise when
the tire is out in the sun or exposed to the sun. In both cases, thermal energy and temperature
of the air are raised. In the first case, the work done in pumping was converted to thermal
energy. In the second case, the rise in temperature was due to energy transferred from the sun
to the tire. We can therefore use the term heat when there is a transfer of thermal energy from
one body to another body at different temperature.
Generally, the heat supplied to the body results in a change in kinetic and potential energies of
the body. Mathematically :
Q = ∆ U + ∆ EK
Where Q is the heat supplied , ∆EK
to a body and ∆U are changes in kinetic and potential
energies of the body. Therefore heat is not a stored energy instead its energy in transit by
means of temperature differences. Since heat is a form of energy, its SI Joule .The quantity
of heat needed to raise the temperature of 1g of water by one degree Celsius varies slightly
for different water temperatures.
1 cal = 4.2 J
Measurement of temperature
, Temperature Scale
The Celsius Scale: Previously known as the centigrade scale, is constructed by defining
the ice-point temperature to be zero degrees celsius (00c ) and the steam-point
temperature to be 1000 c . The space on the glass tube between the ice-point mark and the
steam point mark is then divided into hundred equal intervals or degrees, and the degree
markings are extended below the ice-point mark and above the steam-point mark.
The Fahrenheit Scale: is conducted by defining the ice-point temperature to be 320F
and the steam-point temperature to be 2120F . Note that there are 100 Celsius degrees and
180 Fahrenheit degrees between the ice-point and the steam-point. A temperature change
of one Fahrenheit degree is therefore smaller than a change of one celsius degree . A
temperature of one celsius degree equals a change of 9/5 Fahrenheit degrees. To convert a
temperature given on one scale, we must also take into account the fact that the zero
temperatures of the two scales are not the same. The general relation between a Fahrenheit
temperature tF and a Celsius temperature tC is
EXAMPLE 1:
Find the temperature on the celsius scale equivalent to 500F.
Ans.
Based on the above equation,We obtain:
Substituting the values,
EXAMPLE 2:
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