Summary Notes AQA A-level Physics Paper 3 - Thermodynamics

Internal
Energy
Sum of kinetic and
potential energy of the
particles
For an ideal
gas:
U ENGT,
=



absolute
at zero v 0,=
k. E =
0




Thermal equilibrium no =

heattransfer
net




Zeroth law:two objects which are in thermal equilibrium with a
third,
with
be
must in thermal equilibrium each other


workis
If done, to of the
objects increases due to increased internal
There
energy. is no
heating. E.g compression/expansion of a
gas

FirstLaw
if+, work is done BY the
system (gas is
expanding)
① =
AU + W-if-, work is done ON the
system (compression

If the piston moves downwards:
molecules are pushed together
Udue
·causing an increase
in to

increased K.E and P.E

Volume decreases work done the
gas
-
on


WI-), Q (0) ,
aN(+)


If the pulled outwards If
the held place,
piston is
piston is at




gas expanding, with
work done the work done
is
by no is


If healed:U4as K.E4
energy decreases, AUI)
internal
If cooled:Un K. Eh
Volume
as
work has been done
increases -




by the
gas

, !Qin* -
AU Q-(-w) a
=
=


+ w 3. Q out
--

->
AV = -
q (-
-



w)
Won,- Won W Q
=
-




-


2. AU=R-W
Qins 4. Rout AV = -
Q-W

Why it
Why it




FirstLaw closed Non-flow
systems
~ -
in
processes
intral energy the to
- only depends on



·Assume the ideal
gas is

·Assume work done causes a
change in volume



PV nRT systems allow How
PI=P to
=




a
gas


Isothermal
Changes
ConstantT = AU =0 Q :W

P




·in
194
/2 - 3 isotherm
=




pV=constant, P, U, PzU2 =




the
Work donewarea under the isoturmal move




~
V


TcT2 Q =-W
Compression: -




Expansion:Q W :




Ve VI

Reversible othermal contained walled
is
process:gas is in this highly
conducting vessel (extra workmustbe done)