Chapter 10 – Transfer of thermal energy and its effects

Temperature: Measures how cold or hot an object is.
Heat: Amount of thermal energy transferred from a hot region to a colder region.
Thermal energy always flows from a hotter region to a colder region.
Net flow of thermal energy occurs only when there is a difference in temperature.
SI unit of temperature: Kelvin (K).
Other common units: degree Celsius (°C) and Fahrenheit (°F).
$1 °C ≈ 274.15 K$

Particles lose energy and vibrate less vigorously, hence moving closer to each other.
Distance between particles decreases, thus taking up less space.
Volume of matter decreases, and density of matter increases.
Mass of matter does not change during expansion or contraction.

In general, solids expand and contract less than liquids, while liquids expand and contract less than gases.
Gases have the weakest forces of attraction between particles.
The particles in gases can move much further apart than in liquids and solids, occupying a bigger volume.
Thus, gases expand the most.

Used in thermostats & bimetallic thermometers.
Bimetallic strip consists of two different metals (e.g., brass and steel) bonded together.
Brass expands and contracts more than steel.
- Expansion: Bimetallic strip bends downwards with brass on the outward side and steel on the inward side.
- Contraction: Bimetallic strip bends upwards with brass on the inward side and steel on the outward side.
The metal that expands the most will also contract the most.

Transfer of heat energy without the physical movement of the medium (solids, liquids, or gases).
The particles near the heat source gain thermal energy and start to vibrate more quickly.
They collide with their neighboring particles to transfer energy to them, causing them to start vibrating more quickly.
The process repeats itself until the particles at the colder end are vibrating at the same rate.
Gases are less effective conductors because the particles are far apart, and thus the transfer of energy from more energetic to less energetic particles by colliding cannot take place effectively.
Metals are better conductors because they have delocalized electrons that gain thermal energy from interacting with the particles.
The small size and high speed electrons allow them to move easily and quickly to the cooler end.

Transfer of thermal energy from one place to another by the physical movement of the medium [fluids (liquids and gases)], due to a difference in density.
When the particles near the heat source are heated, the fluid increases in volume (expands), becomes less dense, and rises.
The cooler part of the fluid will be denser than the hotter fluid and will sink to take the place of the hotter fluid that had rose.
In turn, the cooler part of the fluid gets heated by the heat source.
The cycle repeats to set up convection currents.
The convection currents help to transfer the thermal energy evenly until each part of the fluid reaches the same temperature.

Transfer of thermal energy from a hotter body to a cooler body without the need for a medium (can take place in solids, liquids, gases, and vacuum).
All bodies and objects emit infrared radiation.
Thermal energy that is transferred by radiation may be absorbed or reflected.
The hotter the object, the more thermal energy it emits/radiates.
When the object emits/radiates thermal energy via radiation, its temperature decreases.
When the object takes in/absorbs thermal energy via radiation, its temperature increases.

Type of materials
- Different types of materials have different thermal conductivities.
State of matter
- Solids are better conductors than liquids, and liquids are better conductors than gases.

Temperature of object
- The higher the surface temperature of an object compared to the surrounding temperature, the higher the rate of emission of heat.
Surface area of object
- The larger the surface area of an object, the higher the rate of emission or absorption of thermal energy.
Type of surface
- Color and texture of the surface.
  - Dull, rough, and black surfaces are better emitters and absorbers of thermal energy.
  - White, shiny, polished, or silver surfaces are poor emitters and absorbers of thermal energy.

The layer of vacuum between the silvered surfaces in the vacuum flask prevents heat loss by conduction and convection.
Conduction and convection cannot take place in a vacuum.