3. PERPETUAL MOTION MACHINE-I
• First law of thermodynamics says
that energy is conserved
• There can be no machine which
would continuously supply work
without some other form of energy
getting dissipated
• A machine violating this is PMM-I
4. • Physical processes in nature can proceed
toward equilibrium spontaneously:
• Water flows down a waterfall.
• Gases expand from a high pressure to a
low pressure.
• Heat flows from a high temperature to a
low temperature.
5. INTRODUCTION TO II LAW
• Once taken place, a spontaneous
process cannot be reversed by itself.
• Some external inputs, energy, must
be expended to reverse the process.
• As it falls down the waterfall, water
can be collected in a water wheel,
cause a shaft to rotate, coil a rope
onto the shaft, and lift a weight.
6. • Thus the energy of the falling water
is captured as potential energy
increase in the weight, and the first
law of thermodynamics is satisfied.
• There are losses associated with
this process (friction)
• What are the losses?
• IRREVERSIBILITY
7. Spontaneous Processes
• Spontaneous processes
are those that can
proceed without any
outside intervention.
• The gas in vessel B will
spontaneously effuse
into vessel A, but once
the gas is in both
vessels, it will not
spontaneously
9. Spontaneous Processes
• Processes that are spontaneous at one
temperature may be non spontaneous at
other temperatures.
• Above 0C it is spontaneous for ice to
melt.
• Below 0C the reverse process is
spontaneous.
10. Reversible Processes
In a reversible process
the system changes in
such a way that the
system and
surroundings can be
put back in their original
states by exactly
reversing the process.
Changes are
infinitesimally small in
a reversible process.
11. Irreversible Processes
• Irreversible processes cannot be undone by
exactly reversing the change to the system.
• All Spontaneous processes are irreversible.
• All Real processes are irreversible.
12. Model Heat Engine
• Qhot= W+Qcold
or
• Qhot-Qcold=W
(what goes in must
come out)