Thermal Physics Flashcards
Absolute zero
The lowest possible temperature, at which an object has minimum internal energy
What is the absolute scale?
A temperature scale in kelvin, defined in terms of absolute zero, 0K, and the triple point of water, 273K
Absolute temperature
Temperature in Celsius + 273
What is boiling point?
The temperature at which a pure liquid at one atmospheric pressure boils
What is Boyle’s law?
For a fixed mass of gas at constant temperature, it’s pressure x volume is constant
What is the Boltzmann constant?
The molar constant / Avogadro number
What is Brownian motion?
The random and unpredictable motion of a particle such as smoke particle caused by molecules of the surrounding substance colliding at random with the particle
What is Charles’ law?
For an ideal gas at constant pressure, it’s volume is directly proportional to it’s absolute temperature
What is heat (Q)?
Energy transferred due to a difference in temperature
What is heat capacity?
The energy required to change the temperature of a substance by 1K
What is an ideal gas?
A gas under such conditions so that is obeys Boyle’s law
What is the ideal gas equation?
pV=nRT
n= number of moles, R= the molar constant
What is internal energy?
The sum of the random distribution of the kinetic and potential energies of a substance’s molecules
What is the kinetic energy if the molecules in an ideal gas?
Mean kinetic energy = 3/2kT
Total kinetic energy = 3/2nkT
What is the kinetic theory of a gas?
Molecules are in continual random motion so pressure is pV=1/3Nmc^2
What is the latent heat of fusion?
The energy required to change the state of a liquid to solid (or vice versa) without a change in temperature
What is latent heat of vaporisation?
The energy required to change a liquid to a gas (or vice versa) without a change in temperature
What is melting point?
The temperature at which a pure substance’s state changes from a solid to liquid
What is metastable state?
An excited state of the nuclei of an isotopes that lasts long enough after alpha or beta emission for the isotope to be separated from the parent isotope
What is a moderator?
Substance in a thermal nuclear reactor that slows down the fission neutrons so the they can go on to produce further fission
What is the nucleus?
The relatively small part of an atom where all the atom’s positive charge and most of its mass is concentrated (1/10th size of the atom)
What is pair production?
When a gamma photon changes into a particle and antiparticle
What is a photon?
Wave packet of electromagnetic radiation
E=hf
What is the pressure law for an ideal gas?
Its pressure is directly proportional to its absolute temperature
What is sublimation?
The change of state when a solid changes to vapour directly
What is thermal equilibrium?
When no overall heat transfer occurs between two objects at the same temperature
What is specific heat capacity?
The quantity of thermal energy required to raise the temperature of unit mass of a substance by a unit temperature
What is the relationship between temperature and energy transfer?
Temperature determines the direction in which thermal energy will be transferred
Thermal energy is transferred from a region at a higher temperature to a region of lower temperature
Define thermal equilibrium
Regions of equal temperature are in thermal equilibrium, where there is zero resultant energy transfer between them
What factors effect internal energy?
Temperature —> if temp increases, molecules travel more rapidly, KE increases, internal energy increases
Pressure —> (not ideal gas) Pressure decreases (with no change in temp), gas expands, work done on molecules to pull them apart, therefore increase in P.E. and increase in internal energy
State — increase in potential energy
Define an ideal gas
A gas that has internal energy only in the form of random kinetic energy
Define internal energy of a body
The sum of the random distribution of kinetic and potential energies of all the molecules in the body
Pressure =
Force (F) / Area (A)
Define phase
Phase means whether a substance is a solid, liquid or gas
What is the ideal gas equation?
pV = nRT
p = Pressure (Pa) V = Volume (m^3) n = number of moles R = gas constant (8.31 JK^-1 mol^-1) T = temperature (K)
Charles’ Law
The volume occupied by a gas at a constant pressure is directly proprtional to its thermodynamic (absolute) temperature
Boyle’s Law
The pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature remains constant
State three assumptions of the kinetic model of ideal gases
Particles move with random, rapid motion
There are no intermolecular forces
Collisions are elastic
Use kinetic theory of gases to explain how a gas exerts a pressure
Molecules continually collide with the walls of a container
By doing this, force is exerted on the walls of the container
This force is spread over the area of the container, which results in pressure being exerted
State two conclusions about air molecules that may be deduced from Brownian Motion
Smoke molecules are larger than the air molecules
Air molecules are in perpetual random motion at different speeds
Explain the term thermal equilibrium
Where the temperature of the two regions is equal, so there is no net heat exchange
