chapter 14 - thermal physics Flashcards
triple point
3 phases of matter can exist in thermal equilibrium at this point
- water = 0.01ºC @0.64kPa
thermal equilibrium
when two objects are in thermal equilibrium with each other there is no net flow of thermal energy between them
zeroth law - if 2 objects are in thermal equilibrium with a third then they are all in equilibrium eg A and C are in eq with B then A and C are in eq with each other
absolute temperature
T(K) = θ(ºC) + 273
0K = -273ºC
kinetic model
- all substances are made of atoms or molecules
- are arranged differently depending on phase
solid
- regularly arranged, packed close together
- strong electrostatic forces of attraction holding atoms in fixed positions
- (can exhibit SHM - vibrate around equilibrium)
solid to liquid
- solid is heated - atoms gain energy
- vibrate more rigorously (with increasing amplitude) and eventually break away from solid structure
liquid
- atoms still close together + can change position, sliding over each other - more KE
- is still electrostatic forces between atoms but weaker so no fixed structure
liquid to gas
- when heated atoms gain enough energy to break away
gas
- atoms move much faster and are much further apart
- negligible electrostatic forces between them
state change graph
temp against time
diagonal when heating flat when changing states
S>L is shorter than L>G as it taqkes more energy to turn liquid to gas than solid to liquid
specific heat capacity of a block
- set up a block with insulation and heater in connected to ammeter and voltmeter with thermometer in block
- measure mass of block
- record initial temp of block
- insert heater when hot - make sure fully inserted so all energy is transferred
- time 300 secs - noting I and V at regular intervals (to record fluctuations)
- remove heater + measure maximum temp of block
(wait for it to reach thermal equilibrium) - IVt = mcΔT
- plot Tf against time
Tf = (IV/mc)t + Ti
specific heat capacity of block experiment errors
- I and V fluctuations
- mass error balance
- analogue thermometer
- heating of lagging
- immersion heater top heated
internal energy
sum of randomly distributed KE and PE of the atoms or molecules in a substance
- increases by changing temp or state
kinetic energy
movement energy ∝ T (K)
potential energy
electrostatic intermolecular forces
gas PE
0
- negligible forces between atoms
liquid and solid PE
negative
- as energy has to be added to system to free them from bound state
specific heat capacity
energy required to heat 1kg of substance by 1ºK
units - J/kgK
Q = mcΔT
- for all objects
- depends on form - ice or water is diff
power
= E/t
= mcΔT/t = IV
IVt =mcΔT
specific latent heat
2 types - fusion, vaporisation
Lf = specific latent heat of fusion
Lv = specific latent heat of vaporisation
Lv»Lf
Q = mL
Latent heat of vaporisation experiment
- set up kettle connected to power meter and ac source on a balance with a timer
- water in kettle should be at 100ºC - reset power meter when steam appears
- video the experiment with timer and mass scale reading in frame
- record power and mass at time intervals
- plot P against change in m/t
grad = Lv
E = mL
E/t = mL/t
P = Lm/t
Latent heat of vaporisation experiment errors
- water not at 100ºC - use less water - just covering heating element
- not just water heated - kettle is as well - lagging - warmer room so not much difference to surroundings
brownian motion
all particles in a fluid move in random directions at high speeds
changes in direction are due to collisions
observing brownian motion
smoke particles show random motion
- due to collisions with air particles
how to prevent heat losses
lagging/ insulation
cover to prevent evaporation
method of mixtures
- known masses of two substances at diff temps are mixed together
- allow to reach thermal eq and record final temp
- can find c of one if you know c of the other
Latent heat of fusion experiment
set up a funnel filled with ice on top of a beaker
put a heater in the ice with a thermometer and connect to a current voltage circuit
- turn on for a given time
- measure the mass of water that is gained
Lf = IVt/m
