Physics - Recall for Chapter 14; Thermal Physics
Recall Questions
What is the absolute scale of temperature?
A scale used for measuring temperature that uses absolute zero and the triple point of pure water as it fixed points.
What are the units of the thermodynamic (absolute) temperature scale?
Kelvin.
What is a temperature change of 1 K equivalent to?
A temperature change of $1^\circ$.
What is the triple point of a substance?
The temperature and pressure at which a substance can exist in all three phases in thermal equilibrium.
What is thermal equilibrium?
When two objects are at the same temperature so there is no net transfer of thermal energy between them.
What is absolute zero temperature?
The temperature at which the internal energy of a system is at its lowest possible value and is due only to potential energy as particle motion stops.
What is $0^\circ \text{C}$ in Kelvin?
What is the relationship between temperature in degrees and temperature in Kelvin?
What is the relationship between absolute temperature and the average KE of particles in a substance?
Absolute temperature is proportional to average kinetic energy of the particles in a substance.
Describe the kinetic model of a solid?
A regular arrangement of particles that are closely packed and strongly attracted to each other. Particles vibrate about fixed positions but can’t change positions in the structure.
Describe the kinetic model of a liquid?
Particles are attracted to each other but are free to move around each other. Particles have greater KE and PE than in a solid.
Describe the kinetic model of a gas?
Particles are further apart than in a liquid or solid, move freely and rapidly in random directions with random speeds, have negligible forces of attraction and so no potential energy.
What is Brownian motion?
The continuous random motion of small particles suspended in a fluid, caused by collisions between the fluids molecules and the larger particles.
Describe two observations that provide evidence for Brownian motion?
The motion of pollen grades in water and the motion of smoke particles in a smoke cell.
What is the internal energy of a substance?
The sum of the randomly distributed kinetic and potential energies of the particles in an object.
What happens to internal energy, KE and PE during a temperature change?
Internal energy changes, KE changes, PE remains constant.
What happens to internal energy, KE and PE during a state change?
Internal energy changes, KE remains constant, PE changes.
Why doesn’t the temperature of a substance change whilst it is changing state?
The electrostatic potential of the particles is changing rather than the kinetic energy.
Why is the electrostatic potential energy of liquids and solids negative?
Energy must be supplied to the substance to break the bonds between particles.
What effect does increasing the temperature have on the particles in a substance?
It increases their average kinetic energy.
What is the specific heat capacity $c$ of a material?
The energy needed to raise the temperature of $1\text{kg}$ of the material by $1$ degree Celsius/Kelvin without any change of state.
What are the units of specific heat capacity $c$?
What is $\Delta Q$ in $\Delta Q = mc \Delta θ$?
Thermal energy gained (or lost if negative) by an object (provided no change in state).
What is the specific heat capacity of water?
What is the specific latent heat of vaporisation $L$ of a substance?
The energy required to change 1kg of a liquid to a gaseous state with no change in temperature.
What is the specific latent heat of fusion $L$ of a substance?
The energy required to change 1kg of solid to liquid with no change in temperature.
What are the units of latent heat $L$?
Describe briefly how the specific heat capacity of a substance can be determined (long)?
Measure mass of solid using balance. Heat using electrical heater and measure temperature in regular time intervals. Plot graph of temperature against time. Gradient of graph is equal to $VI/mc$.
Describe briefly how the specific latent heat of fusion or vaporisation can be determined (long)?
Using an electric heater to a melt or boil a substance. Measure the mass of liquid collected after melting or condensed after boiling at regular intervals. Plot a graph of mass against time. Gradient of graph is equal to $VI/mL$.
What may an experimentally determined specific heat capacity to be an overestimate?
Energy loss to the surroundings, which can be reduced by insulating the solid
When would you use the equation $E = mc\Delta \theta + mL$?
If an object changes temperature and changes state during heating.