The document discusses two topics: the 2nd law of thermodynamics and the Doppler effect. For the 2nd law of thermodynamics, it defines the Kelvin and Clausius statements, and discusses applications including heat engines like the Carnot engine and steam engine. It explains that heat engines convert thermal energy to mechanical work and discusses the working principles. For the Doppler effect, it defines the phenomenon where the observed frequency of a wave is different for an observer moving relative to its source. It discusses the four cases where the observer or source is moving and provides examples of police radar guns and Doppler radar used in weather monitoring.

1. 2nd
Law of Thermodynamics & its Apps.
Definition[1]
:-
Basically there are two statements of the following law:
KELVIN STATEMENT: - It’s impossible to construct a heat engine which takes
heat from HTR and converts all of this heat into work and having no sink.
CLAUSIUS STATEMENT: - When a process is reversible its net change in entropy
is zero. Hence entropy for reversible process is constant. The entropy change for
irreversible process is always positive. It mean natural process entropy always
increase.
Applications
Heat Engine[2]: - In thermodynamics Heat Engine is a systemthat converts thermal
energy into mechanical energy, which can be used to perform any mechanical work.
In heat engine the engine is basically works like a smokestack. When heat is
generated in the engine it generates high temperature. Generated temperature try
to come out from the engine and during this process the engine start movies and
Energy converted into Mechanical work. This mechanical work is used in other
mechanical works with the help of other mechanical Machines.
1. Carnot Engine [3]: -
Carnot engine theory is given by Sadi Carnot. He was the owner of 2nd law of
thermodynamics.
Before his theory it was consider that working efficiency of Carnot engine dependent
on the fluid used in the engine.
Carnot said that working efficiency of engine is independent on the fluid used in that
engine. But his theory was ignored and stop working on it. The future scientist study
his theories carefully and worked on it
Working of Carnot Engine [4]: - The combustion of fuel takes place due to generation
of the spark as in case of the gasoline engines or due to compression of the fuel as in
case of the diesel engines.
Some part of the heat generated inside the engine is used to perform the work
moving piston inside the engine cylinder. The piston is connected to the crankshaft
via connecting rod. The returning motion of the piston is converted into the rotary
motion of the crankshaft, which is converted to the rotary motion of the wheels via
gear box. The remaining part of the heat generated inside the engine is released to
the atmosphere as the exhaust gases or tailpipe emissions. In this case the engine
where heat is generated is called as source, whereas the atmosphere where heat is
released is called as sink. As per the second law of thermodynamics, higher the

2. temperature of the source and lower the temperature of the sink, higher is the
efficiency of the engine. But it remains still an ideal case.
A heat Engine takes in some fluid across a cycle process where about [5]:
1) The heat is absorbed of one high temperature sources, increasing energy in
machine
2) Change partly energies in this goes to mechanical effort.
3) Discarding residuary energy as a heat goes to low temperature source.
Q=Q1-Q2 W=Q1-Q2
2. SteamEngine [6]: - It is the engine which converts steam engine into
mechanical energy using working fluid.
In 1781 James Watt patented a steam engine that produced continuous rotary
motion. Watt's ten-horsepower engines enabled a wide range of manufacturing
machinery to be powered. The engines could be sited anywhere that water and coal
or wood fuel could be obtained.
Working of Steam engine [7]:-
In a simple engine the charge of steam works only once in a cylinder. It is then
exhausted directly into the atmosphere or into a condenser. As steam expands in a
high-pressure engine its temperature drops because no heat is added to the system.
This is known as adiabatic expansion and results in steam entering the cylinder at
high temperature and leaving at low temperature. This causes a cycle of heating and
cooling of the cylinder with every stroke, which is a source of inefficiency.
3. Cooler Engine [8]: -
The Basic Principal of cooler engine is flowing heat from cool reservoir to hot
reservoir by external effort on the system. This principal is opposite to that of in a
heat engine. The magnitude of external work need in a cooler engine is formulated
as follows:
W=Q1-Q2
Q1= Absorbing of heat from low temperature
Q2= Heat given at high temperature
If the process happening in the cooler engine is reversible then it is called a Carnot
cooler where following equation applies.
Example: Refrigerator
Refrigerator is an Example of 2nd law of thermodynamics. In refrigerator, Hot air
enters through Compressor and compressor pass it to the CO2. CO2 converts the hot
air into cold air and then pass it to the refrigerator. It is the air used for freezing or
cooling in the refrigerator.

3. Doppler Effect
Definition[1]
:- The Doppler Effect is the change in frequency of a wave for an
observer moving relative to its source. I us named after Austrian Physicist Doppler.
The Austrian introduced some cases about the theory about Doppler Effect.
Case 1: When observer is moving away from the source.
Case 2: When observer is moving toward the source.
Case 3: When source is moving away from the observer.
Case 4: When source is moving towards the observer.
Case 1[2]
:When observer is moving away from the source.
When observer start moving away from the source than the frequency of the source
start decreasing which is given by f’, speed of sound is given by v speed of moving
object is given by Vobs .
If V=λf for source than frequency of source is given by:
f’= [(f) v-|Vobs|]/v
Case 2[3]
:When observer is moving towards the source.
When observer start moving towards the source than the frequency of the source
start increasing which is given by f’, speed of sound is given by v speed of moving
object is given by Vobs .
If V=λf for source than frequency of source is given by:
f’= [(f) v+|vobs|]/v
Case 3[4]:When source is moving away from the observer.
When source is moving away from the observer than its frequency start decreasing
which is given by f’.
Speed of sound is given by v speed of moving source is given by Vs.
If V=λf for source than frequency of source is given by:
F’= (fv)/v+|Vs|
Case 4[5]:When source is moving towards the observer.

4. When source is moving away from the observer than its frequency start increasing
which is given by f’, speed of sound is given by v speed of moving source is given by
Vs.
Speed of sound is given by v speed of moving source is given by Vs.
If V=λf for source than frequency of source is given by:
f’= (fv)/v-|Vs|
Applications [6]
Police Radar:
The handheld radar guns used by police to check for speeding vehicles rely on the
Doppler Effect. Here's how they work:
1. A police officer takes a position on the side of the road.
2. The officer aims his radar gun at an approaching vehicle. The gun sends out a burst
of radio waves at a particular frequency.
3. The radio waves strike the vehicle and bounce back toward the radar gun.
4. The radar gun measures the frequency of the returning waves. Because the car is
moving toward the gun, the frequency of the returning waves will be higher than the
frequency of the waves initially transmitted by the gun. The faster the car's speed,
the higher the frequency of the returning wave.
5. The difference between the emitted frequency and the reflected frequency is used
to determine the speed of the vehicle. A computer inside the gun performs the
calculation instantly and displays a speed to the officer.
Doppler radar:
Meteorologists use a similarprinciple to read weather events. In this case, the
stationary transmitter is located in a weather station and the moving object being
studied is a storm system. This is what happens:
1. Radio waves are emitted from a weather station at a specific frequency.
2. The waves are large enough to interact with clouds and other atmospheric objects.
The waves strike objects and bounce back toward the station.
3. If the clouds or precipitation are moving away from the station, the frequency of the
waves reflected back decreases. If the clouds or precipitation are moving toward the
station, the frequency of the waves reflected back increases.

5. 4. Computers in the radar electronically convert Doppler shiftdata about the reflected
radio waves into pictures showing wind speeds and direction.
Reference
2nd
Law of Thermodynamics
1. Punjab Text book
2. Wikipedia.org
3. Tektonics.org
4. Tektonics.org
5. Slideshare.net
6. Wikipedia.org
7. Slide Share.net
8. Slide Share.net
Reference
Doppler Effect
1. Wikipedia.org
2. Punjab Text Book 1st Year
3. Punjab Text Book 1st Year
4. Punjab Text Book 1st Year
5. Punjab Text Book 1st Year
6. Science.Howstuffworks.Com by William Harris