P2 thermal physics Flashcards
distinguishing properties of solids
- fixed shape
- incompressible
- cannot flow
distinguishing properties of liquids
- takes shape from bottom of container
- incompressible
- can flow
distinguishing properties of gases
- completely fill volume of container
- can be compressed
- flows very quickly
term for change in state from solid to liquid
melting
term for change in state from liquid to gas
evaporation
term for change in state from gas to liquid
condensation
term for change in state from liquid to solid
freezing
term for change in state from gas to solid
deposition
term for change in state from solid to gas
sublimation
structure of of particles in solids
- regular arrangement
- particles v close tg
- vibrate in one place
structure of particles in liquids
- irregular arrangement
- particles v close tg (strong intermolecular forces)
- move around randomly and slowly
structure of particles in gas
- irregular arrangement
- particles far apart
- move around randomly and quickly
why are solids difficult to compress
particles already packed v close tg
why cant solids flow
particles held in a fixed, regular arrangement by strong intermolecular forces
why cant liquids be compressed
particles are alr v close tg
why can liquids flow
- intermolecular forces between particles weaker
- can move past each other, positions not fixed
why are gases not dense
- intermolecular forces are extremely weak
- do not attract each other
relationship between temperature and motion of particles
as temp increases, KE of particles increases and motion increases
what does the random motion of particles in a suspension prove
the kinetic particle model of matter // brownian motion
describe and explain brownian motion
- caused by random collisions
- between particles in suspension
- and much smaller, fast-moving particles of fluid
describe pressure of a gas
- impact of rapidly moving gas particles with wall of container
- exerts a force
how does increasing temp change gas pressure (in terms of particles)
- particles gain more KE
- travel faster in random directions
- hit walls of container more often and with greater force
- increase pressure
how does decreasing volume affect gas pressure (in terms of particles)
- decrease distance gas particles have to travel between collisions with walls
- number of collisions between gas particles and walls of container increases
- therefore increase in pressure
describe thermal expansion in terms of particles
- increase temp = increase KE, increase mvmt
- in solid, move further apart, v increase
- in fluids, particles move faster and more freely, v increase
melting and boiling point of water
0, 100
describe condensation in terms of particles
- temp decrease, gas cools
- reach boiling point, temp decrease stop
- forces between particles become stronger, become closer tg
describe solidification (freezing) in terms of particles
- temp decrease, liquid cools
- reach freezing point, temp decrease stop
- forces between particles become much stronger, can no longer move about, fixed positions
describe evaporation in terms of particles
more energetic particles escape from surface of liquid
how does evaporation affect temperature of liquid
- fastest particles with most KE escape first
- mean speed/energy of remaining particles decrease
- temperature of remaining liquid decreases
factors affecting evaporation
- temperature
- surface area
- air movement over a surface
how does temperature affect evaporation
- only particles with enough speed/energy can evaporate
- increase temp = increase mean speed/energy of particles in liquid
- more particles moving fast enough / enough energy to escape
- rate increase
how does surface are affect evaporation
- only particles near surface of liquid can evaporate
- increase number of particles near surface
- increase rate
how does air movement over a surface affect evaporation
- when evaporate, escaped particles form saturated vapour above surface of liquid
- slows rate at which escape
- increase air flow = remove evaporated particles, easier for more particles to escape
- increase rate
differences between boiling and evaporation
- boiling occurs at fixed temperature, evaporation may occur at any temp between melting and boiling point
- boiling happens throughout liquid, evaporation only at surface
typical good thermal conductors
metals
typical bad thermal conductors
non-metals
- plastics
- glass
what are bad thermal conductors known as
thermal insulators
describe thermal conduction in solid non-metals in terms of particles
- vibration of particles in fixed lattice
- increase in temperature in one part, vibration passed on to neighbouring particles
- gradually causes increased vibration/temperature across all material
describe thermal conduction in metals in terms of particles, excluding lattice vibration
- delocalised electrons (in metals) not fixed in place
- able to move quickly, colliding with atoms and causing increased vibration, raising temp
what states of matter does convection occur in
liquids and gases
describe convection in terms of particles and density
- when part of fluid heated, expand, particles move further apart
- region less dense than surroundings, rise upwards
- reach surface, gradually cool, density increase
- sink back down, especially if another part of fluid still being heated and rising upwards
process repeats
does thermal radiation require a medium
no
how does thermal radiation travel
infrared radiation
how does radiation affect temperature of the earth
- emit > absorb: cool
- absorb > emit: warm
- emit = absorb: constant temp
how does surface colour affect emission of radiation and how does it affect cooling
- black surface better emitter
- white surface worse
therefore black objects cool more quickly
how does surface colour affect absorption and reflection of thermal radiation
- black surfaces good absorbers, poor reflectors
- white surfaces poor absorbers, good reflectors
how does texture affect emission of thermal radiation
- dull: better emitters
- shiny: worse emitters
how does texture affect absorption and reflection of thermal radiation
- shiny (very smooth), increase reflectiveness, not good at absorption
- dull, decrease reflection, increase absorption
describe an experiment to distinguish good/bad emitters of thermal radiation
- place Leslie’s cube on heat-resistant surface, fill with freshly boiled water
- point IR thermometer at each surface in turn to measure temp
describe an experiment to distinguish good/bad absorbers of thermal radiation
- attach drawing pins to two diff coloured metal surfaces using petroleum jelly
- place surfaces equal distance from IR lamp or radiant heater
- turn on heater
- observe which surface warms up most quickly by noting which pin falls first
