2nd year phy ch 11 by Syeda fatima rizvi

1. THERMODYNAMICS
• FIRST LAW OF THERMODYNAMICS
• APPLICATIONS OF FIRST LAW OF THERMODYNAMICS

2. THERMODYNAMICS
 Thermo means heat or energy in transit and dynamics relates to movement.
Thermodynamics is the study of movement of energy.
 Thermodynamics is the branch of physics that studies the heat in motion.
 Thermodynamics is the branch of physics that shows the relationship between
heat energy and mechanical work.
 Thermodynamics is the branch of physics that studies the effect of changes in
temperature, pressure and volume on physical system at the microscopic scale by
analyzing the collective motion of their particles.
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3. FIRST LAW OF THERMODYNAMICS
It states that:
“The heat energy supplied to a system equals to the sum of the increase in
internal energy of the system and the external work done by the system”.
∆𝑄 = ∆𝑈 + ∆𝑊
EXPLAIN:
When heat energy is supplied to a fixed mass of gas, its temperature increase causing
an increase in internal energy, the gas expands. If the external work done by the gas
than,
∆𝑄 = ∆𝑈 + ∆𝑊
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4. WORK DONE BY HEAT
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Consider a system consisting of the gas in a cylinder. Suppose that the
pressure of the gas “ P ” and volume “ V ”. If the gas heated by supplying
some amount of heat “Q ” then gas expand by pushing the piston a
small distance “y ” as shown in figure, Then the external work done by
the gas is,

5. APPLICATION OF FIRST LAW OF
THERMODYNAMICS
 ISOBARIC PROCESS
“ A thermodynamic process in which the pressure of the system remains constant
( this is usually obtained by allowed the volume to expand or contract ) during the
supply of heat is called Isobaric Process ”.
EXAMPLE
The simplest example of isobaric process is heating of water in an open
Vessel and a expansion of a gas in a cylinder with a freely moving piston.
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6. APPLICATION OF FIRST LAW OF
THERMODYNAMICS
ISOCHORIC PROCESS
“ A thermodynamic process in which the volume of the system remains constant
during the supply of heat is called Isochoric Process ”.
Isochoric process is also known as isometric process.
EXAMPLE:
Cooking food in pressure cooker is one of the common practical
Example of isochoric process.
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7. APPLICATION OF FIRST LAW OF
THERMODYNAMICS
ISOTHERMAL PROCESS
“A thermodynamic process in which the temperature of the
system remains constant during the supply of heat is
called Isothermal Process ”
EXAMPLES:
Practically isothermal process are hard to find. But a very famous
Example of this process is phase change, b/c transferred of heat
Just change the state of substance and does not change the temperature.
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9. APPLICATION OF FIRST LAW OF
THERMODYNAMICS
ADIABATIC PROCESS
“ A thermodynamic process in which there is no heat transfer
into or out of the system (Q = 0 ) is called Adiabatic Process ”.
EXAMPLES:
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10. QUESTIONS & DISCUSSION
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