Thermal Physics

Question 1

heat capacity definition

Answer 1

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

Question 2

energy required to raise temperature of sample formula

Answer 2

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

Question 3

energy required to raise temperature of specific mass of sample formula

Answer 3

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

Question 4

power definition and formula

Answer 4

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

Question 5

how heat flows

Answer 5

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

Question 6

melting

Answer 6

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)

Question 7

boiling

Answer 7

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)

Question 8

why temperature doesn’t increase during melting or boiling

Answer 8

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

Question 9

latent heat definition

Answer 9

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

Question 10

latent heat of fusion definition

Answer 10

latent heat when converting from solid to liquid or vice versa

Question 11

latent heat of vaporisation definition

Answer 11

latent heat when converting from liquid to gas or vice versa

Question 12

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

Answer 12

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

Question 13

factors affecting rate of condensation

Answer 13

temperature
Surface temperature
airflow
density

Question 14

how temperature affects rate of condensation

Answer 14

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

Question 15

how surface temperature affects rate of condensation

Answer 15

as it decreases, rate of cond. increases

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

Question 16

how airflow affects rate of condensation

Answer 16

as it becomes slower, rate of cond. decreases

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

Question 17

how density affects rate of condensation

Answer 17

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

Question 18

how condensation occurs

Answer 18

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

Question 19

how evaporation occurs

Answer 19

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

Question 20

why evaporation leads to cooling

Answer 20

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

Question 21

factors affecting rate of evaporation

Answer 21

temperature
airflow
density
surface area

Question 22

how temperature affects rate of evap.

Answer 22

rate of evap. increases when temp. of liquid increases

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

Question 23

how airflow affects rate of evap.

Answer 23

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

Question 24

how density affects rate of evap.

Answer 24

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

Question 25

how surface area affects rate of evap.

Answer 25

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

Question 26

conduction of heat definition

Answer 26

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

Question 27

factors affecting rate of conduction

Answer 27

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)

Question 28

why metals good heat conductors

Answer 28

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

Question 29

insulators

Answer 29

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)

Question 30

fluid definition

Answer 30

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

Question 31

convection definition

Answer 31

method of transporting heat through a fluid due to particle movement

Question 32

convection mechanism

Answer 32

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

Question 33

convection current definition

Answer 33

currents of moving fluids

Question 34

how you stay warm with jumper/blanket

Answer 34

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

Question 35

heat radiation definition

Answer 35

emission of electromagnetic waves from warm bodies | doesn’t require a medium to travel through

Question 36

heat radiation features

Answer 36

doesn’t require a medium to travel through

Question 37

surfaces and absorbing and emitting infrared radiation

Answer 37

dark matt surfaces > bright glossy surfaces | best absorbers and emitters of infrared radiation as black absorbs all colours and matt surfaces reflect light less

Question 38

why objects become hotter/colder

Answer 38

emit more/less radiation than it absorbs | proportional to how hot it is

Question 39

reducing heat transfers in vacuum flask

Answer 39

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

Question 40

biology of heat exchange

Answer 40

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

Question 41

animal adaptations in extreme conditions

Answer 41

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)

Question 42

density definition and formula

Answer 42

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

Question 43

how buoyancy depends on density

Answer 43

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

Question 44

how to measure volume of irregular shaped object

Answer 44

place object into beaker of water | find volume of displaced water

Question 45

density and states of matter

Answer 45

solid > liquid > gas | except for water