Thermodynamics

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Chapter 6

• Thermodynamics

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Thermodynamics deals with those processes
related to the use of heat in practical
applications. Ques. 1 Can energy be
recycled? Ques. 2 Is it possible do get more
usable energy out of a process than was put
into it? When a system is doing work for us, we
say that the work done is positive. When we do
work on a system, we say that the work is
negative. internal energy the total energy
(kinetic and potential) of all the atoms that
make up a substance
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First Law of Thermodynamics
Whenever heat is added to a system, it
transforms to an equal amount of some other form
of energy. Heat input equals the increase in
internal energy plus the work output. heat
added increase in external work done
internal energy by the
system The first law of thermodynamics is the
thermal version of the law of conservation of
energy.
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Second Law of Thermodynamics
Heat will never of itself flow from a cold
object to a hot object. Heat can be made to flow
the other way, but only by imposing external
effort. Without external effort, the direction
of heat flow is from hot to cold.
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There is a natural drive toward random
disorder. Any system left alone, tends toward
disorder. entropy a thermodynamic measure of
disorder The entropy of an isolated system
always increases during any spontaneous process
the degree of disorder always increases.
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Chapter 7

• Wave Motion
• Sound

A wave is a wiggle in space and time a
disturbance that repeats regularly in space and
time and that is transmitted progressively from
one place in a medium to the next with no actual
transport of matter.
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Types of Waves
transverse wave A wave with vibration at
right angles to the direction the wave is
traveling. Fig. 7.1 When the end of a coiled
spring is shaken up and down, a transverse wave
is produced. longitudinal wave A wave in which
the vibration is in the same direction as that in
which the wave is traveling. Fig. 7.2 When the
end of a coiled spring is shaken in and out, a
longitudinal wave is produced. A longitudinal
wave is also called a compressional wave.
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The general pattern for a wave is a sine
curve. The same kind of graph can be used to
visualize both transverse and longitudinal
waves.
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Four Wave Characteristics
amplitude the height of the wave measured
from the origin to its crest wavelength (?) the
distance between successive crests of the
wave frequency (f) the number of waves that pass
a certain point in a given amount of time
(cycles/second Hz) speed the distance
traveled by a wave in a given time interval
speed (wavelength)(frequency) v ?f

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The source of any sound is a vibrating
object. When an object vibrates, it disturbs the
air near it, and this disturbance moving through
the air is what is referred to as a sound wave.
When one prong of the tuning fork moves to
the right, air molecules near the fork are
forced more closely together than normal
(condensations). When the prong swings to the
left, air molecules are not squeezed together as
closely as normal (rarefaction). Sound is an
example of a longitudinal wave.
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Speed of Sound
The speed of sound through air at 0 C is 331
m/s. Sound travels fastest through a solid, next
fastest a liquid, and slowest through a gas.
Sound does not travel through a vacuum. The
speed of sound increases with an increase in
temperature.
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A longitudinal disturbance traveling through
the air is called a sound wave only if its
frequency is between 20 and 20,000 Hz because it
is only within this range that the normal human
ear is sensitive. Waves having a frequency
greater than 20,000 Hz are called ultrasonic
waves. The faintest sound that the human ear can
detect, is called the threshold of hearing, and
the loudest sound that the ear can tolerate is
called the threshold of pain.
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A characteristic of all types of waves is that
they can interact with one another. constructive
interference when two waves interfere such that
crest meets crest and trough meets trough The
resultant wave has the same frequency and
wavelength as the two interfering waves but its
amplitude is the sum of the amplitudes of the
two waves. Fig. 7.12 destructive interference
The crest of one wave matches up with the trough
of the other wave. When these two waves come
together, they cancel each other. Fig. 7.13
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The Doppler Effect
The pitch of sound is greater when the source
moves toward you, and less when the source moves
away. The change in frequency due to the motion
of the source is called the Doppler effect. The
greater the speed of the source, the greater will
be the Doppler effect.