Thermal Physics

Question 1

zeroth law of thermodynamics

Answer 1

if C is initially in thermal equilibrium with both A and B, then A and B are also in thermal equilibrium with each other

Question 2

two systems are in thermal equilibrium if and only if

Answer 2

they have the same temperature

Question 3

absolute temperature is linearly proportional to

Answer 3

the gas pressure

T2/T1=p2/p1

Question 4

converting celsius to kelvin

Answer 4

Tk=Tc+273.15

Question 5

for a gas at constant volume, pressure is proportional to

Answer 5

temperature

this gives a temperature scale

Question 6

most materials will

Answer 6

expand when heated and contract when cooled

Question 7

units of the coefficient of linear expansion

Answer 7

per kelvin (or per degree Celsius)

Question 8

what also increases when temperature increases

Answer 8

the average distance between atoms

Question 9

what happens to material with hole in it when heated

Answer 9

hole expands too

Question 10

comparing linear and volume expansion

Answer 10

beta = 3 alpha

Question 11

thermal expansion of water

Answer 11

unusual variation with temperature

water is most dense at 4 degrees celsius

Question 12

thermal stress will develop if

Answer 12

the ends of a rod are rigidly clamped and then the rod heated or cooled

Question 13

fractional change if the rod were not clamped

Answer 13

Δl/l0 = alpha ΔT

Question 14

what to use to calculate tension

Answer 14

young’s modulus

Y=(F/A)/(ΔL/L0)

Question 15

Young’s modulus of material describes

Answer 15

how easy it is to stretch or compress

Question 16

heat flow/ heat transfer

Answer 16

energy transfer that takes place solely because of a temperature difference

energy transferred in this way - heat

Question 17

both work and heat change the

Answer 17

internal energy of a body

ΔU=Q-W

Question 18

calorie

Answer 18

the amount of heat required to raise the temperature of 1g of water from 14.5 degrees celsius to 15.5 degrees celsius

Question 19

unit of heat

Answer 19

joule

Question 20

amount of heat needed to raise the temperature of a mass of material is proportional to

Answer 20

mass
temperature change
constant of proportionality is the specific heat capacity

Question 21

mole

Answer 21

SI unit of amount of substance

one mole contains 6.02*10^23 elementary entities (avogadro constant)

Question 22

molar mass M

Answer 22

mass per mole

so total mass m=nM

Question 23

molar heat capacity

Answer 23

sometimes more convenient to describe quantity of material in terms of moles rather than mass

Question 24

elemental solids tend to have the same molar heat capacity of around

Answer 24

25 J/mole/kelvin

Question 25

dulong-petit law

Answer 25

heat capacity for solids depends on number of particles, related to energy one vibrating atom has Molar heat capacity is C=3R =(approx) 25J/mole/kelvin R is the molar gas constant

Question 26

phase

Answer 26

a specific state of matter such as solid, liquid, gas

Question 27

for a given pressure, a phase change takes place at

Answer 27

a definite temperature

Question 28

phase changes usually involve

Answer 28

change in volume and pressure absorption/emission of heat - latent heat

Question 29

latent heat of fusion

Answer 29

to change 1kg of ice at 0 degrees C to 1kg of liquid water at 0 degrees C at normal atmospheric pressure, you need 3.34*10^5J of heat

Question 30

in general, heat for a phase transition is

Answer 30

Q=+/-mL L -latent heat

Question 31

condensation

Answer 31

gas to liquid

Question 32

vaporisation

Answer 32

liquid to gas

Question 33

freezing

Answer 33

liquid to solid

Question 34

melting

Answer 34

solid to liquid

Question 35

sublimation

Answer 35

solid to gas

Question 36

deposition

Answer 36

gas to solid

Question 37

gas-liquid latent heat

Answer 37

latent heat of Vaporisation

Question 38

liquid-solid latent heat

Answer 38

latent heat of fusion

Question 39

solid-gas latent heat

Answer 39

latent heat of sublimation

Question 40

compare latent heat of vaporisation with latent heat of fusion

Answer 40

Lv>Lf

Question 41

calorimetry

Answer 41

measurement of heat heat needed to raise temp and enable phase transitions temp constant during transitions

Question 42

supercooling

Answer 42

very pure water can be cooled below 0 without freezing resulting state is unstable and known as supercooled disturbance/impurity to condense around can trigger phase transition

Question 43

for heat to flow between regions, there must be

Answer 43

a temperature difference

Question 44

heat always flows from

Answer 44

hot to cold

Question 45

heat current

Answer 45

dQ/dt

Question 46

how is heat transferred in conduction

Answer 46

through transfer of energy between atoms

Question 47

kinetic energy transfer

Answer 47

vibrations in a material carry energy vibrations propagate through materials some energy also carried by free electrons

Question 48

heat current proportional to

Answer 48

ΔT A 1/l

Question 49

constant of proportionality in H=-kAΔT/l

Answer 49

thermal conductivity units W/m/k

Question 50

if the heat flow along the length of the rod is not constant

Answer 50

heat current depends on temperature gradient H=-kAdT/dx -ve indicates heat flows in direction of decreasing temp

Question 51

thermal resistance

Answer 51

defined so that the heat current through the slab is H=-AΔT/Rt Rt=l/k units km^2W^-1

Question 52

a larger thermal resistance means

Answer 52

a better insulator

Question 53

convection

Answer 53

transfer of heat by mass motion of a fluid from one region to another

Question 54

natural convection arises through

Answer 54

differences in density due to thermal expansion

Question 55

heat current due to convection is

Answer 55

directly proportional to surface area

Question 56

forced flow

Answer 56

eg hair dryer

Question 57

free flow

Answer 57

driven by changes in density, eg radiator

Question 58

convection heat current

Answer 58

H=-hAΔT heat traansfer coefficient also depends on temp difference depending on nature of flow

Question 59

free laminar flow

Answer 59

h proportional to |ΔT|^1/4

Question 60

turbulent flow

Answer 60

h proportional to |ΔT|^1/3

Question 61

what slows natural convection near a stationary surface

Answer 61

viscosity of fluids gives an insulating surface film, thinner for forced convection

Question 62

radiation

Answer 62

transfer of heat by EM waves dominant mechanism when feel sun on skin

Question 63

every object emits energy at room temp, this is mostly

Answer 63

infrared

Question 64

as temp rises, wavelength

Answer 64

shifts to shorter values

Question 65

radiation heat current depends on

Answer 65

surface area, surface temp and emissivity

Question 66

emissivity

Answer 66

ratio of emission to that of an ideal emitter

Question 67

if in thermal equilibrium, rates of absorption and emission

Answer 67

must be equal

Question 68

black body

Answer 68

ideal radiator (and absorber) would have emissivity 1

Question 69

ideal reflector

Answer 69

emissivity 0 absorb/emit no radiation at all (why vacuum flasks are silvered)

Question 70

state variables

Answer 70

quantities such as pressure, volume, temp, mass variables that can be used to describe the conditions in which a material can exist

Question 71

equation of state

Answer 71

relationship between state variables eg: ideal gas law

Question 72

ideal gases

Answer 72

volume proportional to no of moles volume inversely prop. to pressure pressure prop. to absolute temp

Question 73

ideal gas equation

Answer 73

pV=nRT

Question 74

for real gases, ideal gas equation holds best at...

Answer 74

low number densities

Question 75

ideal gas equation applications

Answer 75

breathing (diaphragm contracts; lungs expand, vice versa for exhalation) constant volume gas thermometer

Question 76

van der waals equation

Answer 76

tries to take into account the finite size of molecules and interactions between them a accounts for attractive forces b for finite size

Question 77

van der waals - attractive forces

Answer 77

pull gas molecules together, reducing pressure exerted on walls by has

Question 78

van der waals - finite size

Answer 78

this reduces the total volume in which molecules can move around

Question 79

molecules and intermolecular forces

Answer 79

molecules not point-like charges so interaction is more complicated

Question 80

intermolecular force at large distance

Answer 80

attractive

Question 81

intermolecular force at small distance

Answer 81

repulsive

Question 82

force and potential related by

Answer 82

Fr=-dU/dr

Question 83

isotherms

Answer 83

lines of constant temperature (on pressure-volume diagram)

Question 84

when gas molecules are forced close together, attractive forces can get stronger which leads to

Answer 84

phase change (formation of liquid or solid)

Question 85

raising temperature of molecules

Answer 85

more energy so their motion can more easily break the bonds