Lecture 1 - What is temperature? (DOBSON) Flashcards
What is temperature?
A measurement of one type of energy that exists in a substance. This can be considered to be the kinetic energy possessed by the atoms and molecules.
Increasing the kinetic energy of gas atoms does what?
Increases their velocity
In a non-atomic gas how is the energy used?
It is possible that some of the energy is used in making molecules vibrate and rotate - i.e. not all of the energy translates into velocity.
What causes solids to melt/decompose?
Increased temps cause the atoms to oscillate more vigorously around their central positions, as the vibrations become larger, eventually they will overcome the bonds between atoms/molecules.
What is heat?
The flow of energy that results from temperature gradients.
What is heat transfer?
Heat transfer attempts to address thermal behaviour in transient systems by calculating the rate of heat exchange.
What is Fourier’s Law?
(The Law of Heat Conduction): states that the time rate of heat transfer through a material is proportional to the gradient and area (and perpendicular to heat flow):
q_x/A directly proportional to dT/dx.
What is convection?
Movement of any fluid in contact with a surface will impact on the thermal gradient depending on the direction of the gradient it will either transport heat to or from the interface. This maximises the thermal gradient and so maximises the heat flux (rate of heat transfer).
What is conduction?
When rapidly moving or vibrating molecules or atoms interact with neighbouring particles, transferring some of their kinetic energy.
Why are fluids less conductive?
Fluids (especially gases) are less conductive because their atoms are largely spaced out, meaning there are fewer collisions within a certain time compared to solids. Conductivity of gases increases with temp due to faster movement of atoms.
How does conductivity vary with pressure in gases?
DRAW DIAGRAM. Conductivity increases with increasing pressure from vacuum up to a critical point that the density of the gas is such that molecules of the gas may be expected to collide with one another before they transfer heat from one surface to another.
Why is conduction greater in solids?
Because the network of relatively fixed spatial relationships between atoms helps to transfer energy between them by vibration.
What is thermal radiation?
The emission of electromagnetic waves from all matter that has a temp greater than absolute zero. It represents a conversion of thermal energy into electromagnetic energy.
What is the physics behind thermal radiation?
Atoms and molecules are composed of charged particles and their oscillation result in the electrodynamic generation of coupled electric and magnetic fields, resulting in the emission of photons. Electromagnetic radiation, or light, does not require the presence of matter to propagate and travels in the vacuum of space infinitely far if unobstructed. If this light is absorbed by another surface, that surface heats up.
