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BMAT Physics > Thermal Physics > Flashcards

Thermal Physics Flashcards

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1
Q

heat capacity definition

A

amount of energy required to raise temperature of sample by 1 Kelvin

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2
Q

energy required to raise temperature of sample formula

A

energy required to raise temperature of sample = heat capacity (K/J) x difference in temperature (K, °C)
Q = C x ∆T

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3
Q

energy required to raise temperature of specific mass of sample formula

A

energy required to raise temperature of mass of sample (J) = heat capacity (J/K) x mass (kg) x difference in temperature (K, °C)
Q = C x M x ∆T

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4
Q

power definition and formula

A

rate of energy change
power (W) = energy emitted (Q) / time (s)
P = Q / t

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5
Q

how heat flows

A

hotter object to cooler object
greater difference = faster rate of cooling
energy is transferred

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6
Q

melting

A

heat is added
particles given energy
particles are in fixed position and vibrate
adding sufficient heat causes particles to move faster to break bonds holding them (becomes liquid)

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7
Q

boiling

A

liquid heated
particles gain energy, move faster about their container and liquid expands
interactions between particles become weaker as distance between particles increases
addition of sufficient heat results in liquid expanding where particles interact negligibly (gas)

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8
Q

why temperature doesn’t increase during melting or boiling

A

additional energy is used to break/overcome intermolecular forces
instead of supplying particles with more kinetic energy

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9
Q

latent heat definition

A

amount of energy required to change the state of an object from one state to another
addition/subtraction of heat energy without observation of temperature change

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10
Q

latent heat of fusion definition

A

latent heat when converting from solid to liquid or vice versa

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11
Q

latent heat of vaporisation definition

A

latent heat when converting from liquid to gas or vice versa

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12
Q

amount of energy required to convert given mass from one state to another formula

A

amount of energy required to convert given mass of substance from one state to another (J) = mass of substance (kg) x l (kJkg^-1)
Q = m x l

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13
Q

factors affecting rate of condensation

A

temperature
Surface temperature
airflow
density

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14
Q

how temperature affects rate of condensation

A

as it decreases, rate of cond. increases
particles have lower average energy so
easier and more likely to slow down enough to form liquid

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15
Q

how surface temperature affects rate of condensation

A

as it decreases, rate of cond. increases

cold surface will transfer heat away from gas faster, cooling it quicker and forming condensate faster

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16
Q

how airflow affects rate of condensation

A

as it becomes slower, rate of cond. decreases

as conc. of gas will be higher so more cond. will occur on the surface

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17
Q

how density affects rate of condensation

A

as it increases, rate of cond. increases
forces between particles will be stronger so fewer particles will have enough energy to overcome these forces
more likely to form liquid

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18
Q

how condensation occurs

A

Gas changing to liquid
as gas cools, particles move slower and spend longer in close proximity to each other
intermolecular forces increase as temperature drops
once average temperature is below boiling point, gas particles condense into liquid droplets

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19
Q

how evaporation occurs

A

liquid into gas without boiling
occurs despite temperature of liquid below boiling point and average KE of particles being insufficient to do so
some particles with high KE (above average energy) and travelling toward surface of liquid

20
Q

why evaporation leads to cooling

A

evaporation removes particles with highest energy from liquid
remaining liquid has lower average kinetic energy so lower temperature achieved

21
Q

factors affecting rate of evaporation

A

temperature
airflow
density
surface area

22
Q

how temperature affects rate of evap.

A

rate of evap. increases when temp. of liquid increases

higher temp. = average KE = more particles with enough energy to escape from liquid surface

23
Q

how airflow affects rate of evap.

A

rate of evap. increases when airflow over surface of liquid increases
as conc of evap. substance is lower immediately surrounding liquid
air carries gas away and prevents it from condensing back into liquid so higher net evaporation

24
Q

how density affects rate of evap.

A

rate of evap. increases when density lowers
lower density = particles further apart = forces between particles weaker = more particles with enough energy to overcome them and escape liquid

25
Q

how surface area affects rate of evap.

A

rate of evap. increases as SA increases as more particles nearer the surface, easier to escape liquid

26
Q

conduction of heat definition

A

process by which vibrating particles pass on their KE to neighbouring particles in a material

27
Q

factors affecting rate of conduction

A

tighter neighbouring particles = the more they influence each other = more effective conduction
material (e.g. metals)
state (solid > liquid > gas at due to intermolecular distances)
SA (more room for particles to collide)
temp. difference (heat moves faster with greater temp. diff)
length (longer conductor = longer it takes for heat to pass from one side to another)

28
Q

why metals good heat conductors

A

ions tightly bound with small distance (so more influence) between neighbouring ions
also delocalised electrons can move freely and quickly inside metal and collide with other electrons and ions to transfer energy quickly
electrons from hot regions move through structure and collide with ions and electrons at colder parts

29
Q

insulators

A

no free electrons (can only transfer energy by vibration of neighbouring atoms)
liquids and gases poorer conductors as greater intermolecular distances than solids (so less influence)

30
Q

fluid definition

A

no fixed shape but flows and spreads to fill the shape of the container it occupies

31
Q

convection definition

A

method of transporting heat through a fluid due to particle movement

32
Q

convection mechanism

A

when heated from the bottom, particles gain KE
move more quickly so collide more regularly and move further apart
take up more volume, decreases density
less dense regions of fluids rise and displace colder, denser regions colder denser fluids sink to bottom and be heated, cycle continues

33
Q

convection current definition

A

currents of moving fluids

34
Q

how you stay warm with jumper/blanket

A

body heats fixed amount of air around you
warm air trapped by blanket
without blanket, convection carries away warm air, replaced by colder air

35
Q

heat radiation definition

A

emission of electromagnetic waves from warm bodies

doesn’t require a medium to travel through

36
Q

heat radiation features

A

doesn’t require a medium to travel through

37
Q

surfaces and absorbing and emitting infrared radiation

A

dark matt surfaces > bright glossy surfaces

best absorbers and emitters of infrared radiation as black absorbs all colours and matt surfaces reflect light less

38
Q

why objects become hotter/colder

A

emit more/less radiation than it absorbs

proportional to how hot it is

39
Q

reducing heat transfers in vacuum flask

A

vacuum between container and flask prevents convection and conduction since both need medium to occur
inside and outside of liquid container are shiny (not black) so heat radiation from outside of bottle reflected back out and radiation from liquid reflected back into liquid
bottle supported by insulating foam (conducted little heat to outside as possible)
stopped (made out of insulator) prevents heat transfer by convection by trapping air above liquid

40
Q

biology of heat exchange

A

heat regulated to conserve energy and resources

when cold, hair in mammals skin pull upright to trap layer of insulting air around body (reduced her loss by convection)
also blood vessels constrict around extremities to reduce blood flow there
due to high SA:V ratio, more susceptible to heat loss via radiation

opposite occurs when hot + body sweats for heat loss via evaporation

41
Q

animal adaptations in extreme conditions

A

cold:
fur traps insulating air
thick layer insulating blubber to reduce heat transfer away from body
smaller ears
hot:
thin layers of fur
large ears (higher SA so heat dispersed more effectively by passing blood through dilated blood vessels near surface)

42
Q

density definition and formula

A

measure of mass of a substance per unit volume
density = mass / volume
p = M/V

43
Q

how buoyancy depends on density

A

objects denser then the liquid they are in sink and vice versa

44
Q

how to measure volume of irregular shaped object

A

place object into beaker of water

find volume of displaced water

45
Q

density and states of matter

A

solid > liquid > gas

except for water

BMAT Physics (7 decks)

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