Thermal physics Flashcards
revision (21 cards)
Temperature
Average amount of KE of an object.
Measured using thermometer.
Measured in kelvin, Celsius, faheraniet.
Heat
Total amount of energy pf an object.
Measured in joules and calory using joulemeter, calorimeter.
Temp at which all motion ceases
-237 degree Celsius, Absolute 0, 0K.
For an object to be at constant temperature
It needs to emit the same amount of heat as it takes in.
Formulae of kelvin and Celsius.
k= 273+ degree Celsius.
C= 5/9 [f-32]
Changes of state
Sublimation- solid to gas
Deposition- gas to solid
Melting- solid to liquid
Boiling- liquid to gas
Freezing- liquid to solid
Evaporation- liquid to gas
Quantity of heat
Q∝ mass
Q ∝ △ t
Q= mc△ t
c=SHC(specific heat capacity)
When there is latent heat: Q=mL
There are 2 phenomena: Change in state, Rise in temp.
Q=PT
mc=Heat capacity
Gas laws
Temp ∝ pressure
Temp ∝ volume
Pressure ∝ 1/ volume
P1V1= P2V2
V1/T1=V2/T2
P1V1/T1= CONSTANT
Finding the temperature change
Hot to cold- ti- tf
Cold to hot- tf- ti
Specific heat capacity
The amount of heat to raise the temp of 1 kg of an object by 1 degree Celsius.
J/kg/C.
Evoporation
At any temp
Particles which have high energy move out of the liquid. The bonds break down.
Factors boosting evaporation:
1. Higher temperature.
2. Surface area should be larger.
3. Air or drought so the particles can be dragged away.
Cooling by evaporation
The particles with high energy move out and take away some energy with them. The particles left behind cool down by evaporation.
Cooling by contact
An object is placed in the one that’s evaporating and so to evaporate, it takes energy from the other substance and so cools it down.
Thermal expansion
Rise in volume due to rise in temp.
Practical applications.
Railway tracks expand and so there are gaps between the tracks.
Electrical cables are hung loose so when they contract they still have spaces.
Brownian motion
Random motion of dust particles due to the air particles hitting them.
Gas Brownian motion.
The gas when collides with the container exerts a force on it and the momentum of the gas particle changes.
Conduction
The transfer of heat particle by particle in solids.
In metals, the free moving electrons can also transfer energy.
That is why they are good conductors.
Convection
Relies on density change.
Heat is applied on a corner and as the density of the heated particle changes they move upward and the cooler ones move down.
Forms a convection current.
See breeze- As the land is hotter during the day, the heat from it travels to the sea high in the sky and the cold see air goes to the land. This is known as sea breeze.
Radiation
No medium required.
Infrared radiations.
Black is the best emitter and absorber.
Specifically when its dull.
Boling and evaporation differences
Boiling- Fixed temperature, Bubbles formed, occurs through liquid.
Evaporation- Any random temperature, Occurs only at the surface, No bubbles formed, no external heat.
