10_Thermal processes

Also almost fully Ai generated but this works i think

1. terms

• Thermal contact: objects can transfer energy via heating.
• Thermal equilibrium: objects in thermal contact with no net heat transfer.
• Zeroth law: if A and B are separately in thermal equilibrium with C, then A and B are in thermal equilibrium with each other.
• Temperature: same for all systems in thermal equilibrium; related to average KE of particles.
• Energy transfer by heating: energy transfer due to a temperature difference, from higher to lower temperature.
• Conduction: transfer of energy by heating through a medium or across two media in contact, without flow of medium.
• Convection: transfer of energy by heating through convection currents in a fluid, due to a difference in density.
• Thermal radiation: transfer of energy by heating as EM waves such as infrared.
• Use "internal energy" and "heat transfer", not "thermal energy".

2. Heat Transfer

• Hotter object: avg KE decreases. Colder object: avg KE increases.
• Continues until thermal equilibrium (same temperature).
• Same temperature ≠ same internal energy (differ in mass, state, material).
• Metal feels colder than cardboard at same temperature: better conductor, removes heat from skin faster.

3. Conduction

All solids

• Particles near heat source vibrate more vigorously about fixed positions.
• Collide with neighbours, transferring KE.
• No net movement of particles.

Metals (extra)

• Free electrons gain energy, move faster, diffuse from hotter to colder region.
• Collide with positive metal ions, transferring energy.
• Free electron diffusion = metals are good conductors.

Fluids are poor conductors: particles not closely packed, fewer collisions.

Applications

• Insulators: trapped still air (fur, feathers, double glazing, foam, wool), wooden/plastic handles, sawdust on ice, cup sleeves.
• Conductors: aluminium/steel cookware, copper soldering tip, metal heat sinks.

4. Convection

Key chain: heated fluid expands → less dense → rises; cooler, denser fluid sinks to replace it → convection current.

• Net movement of fluid (unlike conduction).

Applications

• Kettle: coil at bottom; water is a poor conductor, convection heats quickly and evenly.
• Aircon: near ceiling; cold dense air sinks, warm air rises into unit.
• Sea breeze (day): land heats faster; low pressure over land; air moves sea → land.
• Land breeze (night): land cools faster; low pressure over sea; air moves land → sea.

5. Thermal Radiation

• No medium needed; travels through vacuum (how Sun's energy reaches Earth).
• Good emitters = good absorbers. Good reflectors = poor absorbers.
• Net emitter if surface is hotter than surroundings.

Factors

Applications

• Shiny/white: aluminium-painted roofs, white houses, avoid dark clothing in Sun.
• Black: dull black solar panels.
• Solar films: let visible light through, block UV and IR.

6. Vacuum Flask

Annex A: Greenhouse Effect

• Earth: Sun's IR passes through atmosphere → surface absorbs, emits longer-wavelength IR → greenhouse gases (H₂O, CO₂) absorb and re-emit in all directions → excess gases cause global warming.
• Greenhouse: IR passes through glass → soil/plants emit longer-wavelength IR → cannot pass back through glass → heat trapped.