Deck 1 Flashcards
Intensive Macroscopic quantities
Independent of the size of the system. E.g. pressure temperature tension
System
Portion of the universe with a certain measurable quantities (E.g. pressure and volume) which define its equilibrium state
Surroundings
The rest of the universe outside the system
Equilibrium state
No net macroscopic flow of energy or matter. State remains constant unless acted upon externally
Macroscopic
Bog property is visible to the naked eye e.g. tempo, pressure, volume
Microscopic
Positions and velocity is of individual molecules or atoms
Isolated system
No energy and matter exchange with surroundings
Closed system
No matter exchange with surroundings but can exchange energy. Has walls which allows the transfer of thermal energy
Diathermal
Heat can pass through
Adiabatic
No heat can pass through
First law of thermodynamics
Change in internal energy equals work done plus heat transferred
Entropy
A measure of a systems disorder. Quantifies the number of microscopic configurations with given macroscopic quantities
Which way does heat flow
Heat will always flow from hot to cold unless something forces it
Zeroth law of thermodynamics
If system A is initially and thermal equilibrium with system B and B is in thermal equilibrium with C then A must be in thermal equilibrium with C
Macroscopic variables at thermal equalibrium
Remain constant once thermal equilibrium is reached
Extensive macroscopic quantities
Proportional to the size of the system. E.g. volume, length, number of gas molecules
Equilibrium states and state variables
Equilibrium states are defined by pairs of conjugate state of variables, one extensive one intensive and the product always has the dimensions of energy
Functions of state
Any quantity which takes a unique value for an equilibrium state of the system. Eg energy, temp, pressure, volume, energy.
Depends only on current state not how it is formed
Ideal gas
One where atoms/molecules are point like (no size or shape) and noninteracting (no forces exerted on each other)
Isotherm
A curve on a PV diagram for an isothermal process
Isotherm behaviour
At high temperatures isotherms behave similar to an ideal gas
Resistance thermometer
use the electrical resistance of an ideal metal, such as platinum or copper. They’re accurate over a large range but not good at the low end
Gas thermometer
Use a fixed quantity of gas held within a container with a fixed volume. Not very practical but accurate and operate over a large range of temperatures
Constant volume thermometer
Difficult to use but accurate over a wide range so more accurate predictor of temperatures at both extremes
Pyrometer
Used for black bodies. Ideal at high temps (100‘s of degrees) can go down to room temp but useless below that. Relationship with temp is non linear so requires careful calibration
Thermocouples
Measure potential difference at a junction of two metals (typically 10’s of micro volts per kelvin). Dependence on temp not very linear. Very narrow temp range
