Thermal Physics Flashcards
Define specific latent heat of fusion
The energy required per unit mass to change a substance from solid to liquid at a constant temperature
Define specific latent heat of vaporisation
The energy required per unit mass to change a substance from liquid to vapour at a constant temperature
Define Internal Energy
The sum of the random distributions of kinetic and potential energies of all the molecules in a body.
Describe solids, liquids and gases in terms of the spacing, ordering and motion of atoms or molecules
Solid: Small spacing, well ordered (lattice), vibrations
Liquid: Small spacing (few gaps), less well ordered, slow random motion
Gas: Large spacing, no order, fast random motion
Describe an experiment that demonstrates Brownian motion and what this shows
Put some smoke particles in a brightly illuminated glass jar.
They appear as bright specks following a jerky and erratic path.
This is due to collisions between smoke and air particles and shows that air molecules ARE MOVING and have HAPHAZARD, RANDOM motion.
The smoke particles are visible, the air molecules are not so the air molecules must be very small.
The smoke particles are constantly moving so the air molecules must be too.
Where does the input energy go during a change of state?
(Electrical) Potential Energy of the molecules
Describe an electrical experiment to determine the specific heat capacity of a solid or a liquid
Insert electrical heater to solid/liquid and thermometer.
Add ammeter in series and voltmeter across heater.
Measure mass of liquid/solid.
Measure initial and final temp to work out change in temp.
Record I, V & t (with stopwatch) to work out Energy. E=IVt
c=E/m0
Uncertainties: Heat loss so insulate or measure below and above room temp.
Stir liquid
Take into account thermal capacity of vessel if liquid.
What are the basic assumptions of the kinetic theory of gases?
Large number of atoms/molecules
No (gravitational) attraction between molecules so they travel in straight lines between collisions
Collisions of particle-particle and particle-wall are perfectly elastic so no KE is lost.
Time of collisions is negligible.
Vol of particles is negligible compared to vol of whole gas.
Mean translational KE of atom/molecule is proportional to what?
Temperature IN KELVIN (thermodynamic temp) IN IDEAL GAS
How does a gas exert pressure on the walls of a container?
MANY molecules collide with the walls
A change in momentum occurs when molecule(s) collide with (and rebound from) the walls of container
Force on molecule is rate of change of momentum
The force exerted by the molecule(s) on wall is equal to force exerted by the wall on the molecule(s) (by Newton’s third law)
pressure (on wall) = sum of forces (on wall) / area (of wall)
Define specific heat capacity
The energy required to raise the temperature of a unit mass by a unit temperature rise.
State Boyle’s Law
The pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of the gas remains constant.
