Thermal Physics Flashcards
Temperature
Measure of the average KE of the particles in a substance (so temp ∝ KE).
Addition of energy to a substance increases the KE of the individual molecules and, therefore, its temperature (difference in heat and temp lies in the transfer bit).
Units: °C, °F, °K
Instrument: thermometer
Construction of a thermometer
Substance must vary linearly with the addition of energy.
Fixed points or reference marks must be present:
Ice point: point of equilibrium between ice and water (0°C, 32°F, 273K)
Steam point: point of equilibrium between steam and water (100°C, 212°F, 373K)
Calibrations must be equally spaced between degrees.
Conversions
Celsius to Kelvin:
K = °C + 273
Celsius to Fahrenheit:
TF = 9/5TC + 32
TC = 5/9(TF - 32)
Heat
Energy transferred between objects because of temp difference.
Always flows from hotter body to colder.
Form of energy (thermal energy).
Thermal equilibrium
State in which two objects in physical contact with each other achieve the same temp.
At this point, there’s no transfer of heat between the two objects.
States of matter
Solid: Molecules tightly packed, vibrate about fixed positions.
Liquid: Loosely packed, glide/slide around one another.
Gas: Far apart, move randomly.
Methods of heat transfer
Conduction, convection, and radiation.
Conduction
Heat transfer by direct contact of objects: occurs mostly in solids because the molecules are tightly packed together.
Sometimes also occurs in liquids.
Conduction involves a medium of transfer (solid molecules).
Ex. transfer of heat from electric stove to pan, spoon in hot coffee.
Convection
Transfer of heat by the movement of air/water molecules: occurs mostly in liquids and gases.
As air/water gets warm, the molecules at the bottom become lighter and rise and get replaced by the colder ones (convection current).
Requires a medium to occur (liquid/gas molecules).
Ex. heating water up, heating up/cooling of the room, land/sea breeze.
Radiation
Transfer of heat by electromagnetic waves through the vacuum of space.
No medium of transfer required (no contact).
Ex. drying clothes under the sun, warming your hands near the fire.
Phase change
Change from one state of matter to another.
Evaporation - Liquid to gas (ex. boiling of water)
Condensation - Gas to liquid (ex. steam room)
Sublimation - Solid to gas (ex. dry ice)
Melting - Solid to liquid (ex. ice cube melting)
Freezing - Liquid to solid (ex. water to ice cube)
Deposition - Gas to solid (ex. water vapor to snow)
Law of Conservation of Energy
States that energy can neither be created nor destroyed, but can be changed from one form to another.
Gas Laws
Explain the behavior of gases:
- Boyle’s Law
- Charles’s Law
- Pressure (Gay-Lussac’s) Law
Deal with Kelvin (Celsius has negative values: we use Kelvin to avoid getting negative volume/pressure values [impossible]).
All about pressure, temp, and volume: for each of these laws, one of these must remain constant (looks at the relationship between the other two).
Boyle’s Law
At constant temp, pressure is inversely proportional to volume.
Pressure is determined by the molecules hitting the walls, so when they’re given more space, there’s less hitting the walls, and so the pressure decreases.
Formula (the factor that’s constant doesn’t play a role in the formula): P ∝ 1/v
PV = constant
P1V1 = P2V2
(main formula)
*See doc for graphs
Charles’s Law
At constant pressure, volume ∝ temp.
Heat gives the molecules more [kinetic] energy, they hit the walls faster, and the volume increases.
Formula: V ∝ T
V/T = constant
V1/T1 = V2/T2
(main formula)
*See doc for graphs
*-273°C is the coldest Celsius temp (hypothetical [hence the dashed line])
*a ∝ b
a∝1/b → inversely proportional to b/directly proportional to 1/b