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Physics 1 > Thermal Physics > Flashcards

Thermal Physics Flashcards

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1
Q

zeroth law of thermodynamics

A

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

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2
Q

two systems are in thermal equilibrium if and only if

A

they have the same temperature

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3
Q

absolute temperature is linearly proportional to

A

the gas pressure

T2/T1=p2/p1

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4
Q

converting celsius to kelvin

A

Tk=Tc+273.15

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5
Q

for a gas at constant volume, pressure is proportional to

A

temperature

this gives a temperature scale

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6
Q

most materials will

A

expand when heated and contract when cooled

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7
Q

units of the coefficient of linear expansion

A

per kelvin (or per degree Celsius)

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8
Q

what also increases when temperature increases

A

the average distance between atoms

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9
Q

what happens to material with hole in it when heated

A

hole expands too

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10
Q

comparing linear and volume expansion

A

beta = 3 alpha

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11
Q

thermal expansion of water

A

unusual variation with temperature

water is most dense at 4 degrees celsius

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12
Q

thermal stress will develop if

A

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

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13
Q

fractional change if the rod were not clamped

A

Δl/l0 = alpha ΔT

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14
Q

what to use to calculate tension

A

young’s modulus

Y=(F/A)/(ΔL/L0)

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15
Q

Young’s modulus of material describes

A

how easy it is to stretch or compress

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16
Q

heat flow/ heat transfer

A

energy transfer that takes place solely because of a temperature difference

energy transferred in this way - heat

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17
Q

both work and heat change the

A

internal energy of a body

ΔU=Q-W

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18
Q

calorie

A

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

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19
Q

unit of heat

A

joule

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20
Q

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

A

mass
temperature change
constant of proportionality is the specific heat capacity

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21
Q

mole

A

SI unit of amount of substance

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

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22
Q

molar mass M

A

mass per mole

so total mass m=nM

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23
Q

molar heat capacity

A

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

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24
Q

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

A

25 J/mole/kelvin

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25
Q

dulong-petit law

A

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

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26
Q

phase

A

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

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27
Q

for a given pressure, a phase change takes place at

A

a definite temperature

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28
Q

phase changes usually involve

A

change in volume and pressure

absorption/emission of heat - latent heat

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29
Q

latent heat of fusion

A

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

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30
Q

in general, heat for a phase transition is

A

Q=+/-mL

L -latent heat

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31
Q

condensation

A

gas to liquid

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32
Q

vaporisation

A

liquid to gas

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33
Q

freezing

A

liquid to solid

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34
Q

melting

A

solid to liquid

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35
Q

sublimation

A

solid to gas

36
Q

deposition

A

gas to solid

37
Q

gas-liquid latent heat

A

latent heat of Vaporisation

38
Q

liquid-solid latent heat

A

latent heat of fusion

39
Q

solid-gas latent heat

A

latent heat of sublimation

40
Q

compare latent heat of vaporisation with latent heat of fusion

A

Lv>Lf

41
Q

calorimetry

A

measurement of heat

heat needed to raise temp and enable phase transitions

temp constant during transitions

42
Q

supercooling

A

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

43
Q

for heat to flow between regions, there must be

A

a temperature difference

44
Q

heat always flows from

A

hot to cold

45
Q

heat current

A

dQ/dt

46
Q

how is heat transferred in conduction

A

through transfer of energy between atoms

47
Q

kinetic energy transfer

A

vibrations in a material carry energy

vibrations propagate through materials

some energy also carried by free electrons

48
Q

heat current proportional to

A

ΔT
A
1/l

49
Q

constant of proportionality in H=-kAΔT/l

A

thermal conductivity

units W/m/k

50
Q

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

A

heat current depends on temperature gradient

H=-kAdT/dx

-ve indicates heat flows in direction of decreasing temp

51
Q

thermal resistance

A

defined so that the heat current through the slab is

H=-AΔT/Rt

Rt=l/k

units km^2W^-1

52
Q

a larger thermal resistance means

A

a better insulator

53
Q

convection

A

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

54
Q

natural convection arises through

A

differences in density due to thermal expansion

55
Q

heat current due to convection is

A

directly proportional to surface area

56
Q

forced flow

A

eg hair dryer

57
Q

free flow

A

driven by changes in density, eg radiator

58
Q

convection heat current

A

H=-hAΔT

heat traansfer coefficient also depends on temp difference depending on nature of flow

59
Q

free laminar flow

A

h proportional to |ΔT|^1/4

60
Q

turbulent flow

A

h proportional to |ΔT|^1/3

61
Q

what slows natural convection near a stationary surface

A

viscosity of fluids

gives an insulating surface film, thinner for forced convection

62
Q

radiation

A

transfer of heat by EM waves

dominant mechanism when feel sun on skin

63
Q

every object emits energy

at room temp, this is mostly

A

infrared

64
Q

as temp rises, wavelength

A

shifts to shorter values

65
Q

radiation heat current depends on

A

surface area, surface temp and emissivity

66
Q

emissivity

A

ratio of emission to that of an ideal emitter

67
Q

if in thermal equilibrium, rates of absorption and emission

A

must be equal

68
Q

black body

A

ideal radiator (and absorber) would have emissivity 1

69
Q

ideal reflector

A

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

70
Q

state variables

A

quantities such as pressure, volume, temp, mass

variables that can be used to describe the conditions in which a material can exist

71
Q

equation of state

A

relationship between state variables

eg: ideal gas law

72
Q

ideal gases

A

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

73
Q

ideal gas equation

A

pV=nRT

74
Q

for real gases, ideal gas equation holds best at…

A

low number densities

75
Q

ideal gas equation applications

A

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

76
Q

van der waals equation

A

tries to take into account the finite size of molecules and interactions between them

a accounts for attractive forces
b for finite size

77
Q

van der waals - attractive forces

A

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

78
Q

van der waals - finite size

A

this reduces the total volume in which molecules can move around

79
Q

molecules and intermolecular forces

A

molecules not point-like charges so interaction is more complicated

80
Q

intermolecular force at large distance

A

attractive

81
Q

intermolecular force at small distance

A

repulsive

82
Q

force and potential related by

A

Fr=-dU/dr

83
Q

isotherms

A

lines of constant temperature

(on pressure-volume diagram)

84
Q

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

A

phase change

(formation of liquid or solid)

85
Q

raising temperature of molecules

A

more energy so their motion can more easily break the bonds

Physics 1 (10 decks)

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