Temperature is the average effect of intermolecular vibrations in matter. EM radiation causes the vibrations to increase, but isn’t directly responsible for temperature. When an object is heated by convection, energy is imparted my collisions between the object’s molecules and the molecules of the convection medium. Is this correct? Do intramolecular vibrations play a part? How do photons play a part in the collisions?
Thanks for your help,
Rob
What you are describing are the qualitative effects of temperature, i.e. vibration of atoms or molecules; however, from a fundamental point of view, the concept of temperature is somewhat different. Depending on how you are looking at a system, temperature may be a measure of the heat concentration or specific heat of a system (1st law), how much energy is available from a system to do work (2nd law), the displacement from thermal equilibrium or state of energy disorder/dispersal (entropy) (3rd law), or the excitation state of a blackbody system (Maxwellian electrodynamics in classical mechanics and Special Relativity), or the fundamental free energy state of a quantized system (quantum electrodynamics, thermodynamics of black holes). It’s not just normal matter that can have temperature; systems comprising entirely of photons or other massless particles can have a temperature, as can a black hole. In these cases, the temperature is based on its blackbody radiation properties of the system in question rather than physical vibration. However, temperature implies an ability to exchange energy via electromagnetic interaction (i.e. exchanges of photons or virtual photons); particles that don’t experience the electromagnetic force cannot contribute to the thermodynamic state of a system and therefore can’t be said to have temperature, even though they can carry energy.
To answer your question about “intramolecular vibrations”, the strength and character of chemical bonds changes with system temperature, so the amount of energy stored in the bond is related to the temperature (which gives rise to latent heat or enthalpy of a substance at state and phase transitions); however, a bond can have different characteristics at the same measured temperature depending on what direction energy is flowing into or out of they system. Whether the vibrations are intramolecular or intermolecular is irrelevant, although most bonds that define a molecule are covalent (very strong) in nature, and thus the concept of vibration within a molecular structure is not as intuitive as the conception of molecules in a fluid physically vibrating in and out of ionic or van der Waals bonds. The concept of thermal vibration in metallic lattices is even more complicated, referring as it does to the motion of electrons as a kind of quantum mechanical gas loosely and yet securely tied via metallic bonds.
Sorry that this wasn’t a simple answer, but I’m trying to answer the gist of your question without rambling into the esoterica of quantum thermodynamics. The notion of temperature as the rate at which particles are vibrating is sufficient for understanding virtually all everyday phenomena, but is neither pedantically correct nor does it really convey the true concept of temperature in the abstract sense that a theoretical thermodynamicist or physicist would use.
Stranger