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Physics 2A > Thermal Physics > Flashcards

Thermal Physics Flashcards

1
Q

What is the zeroth law of thermal dynamics?

A

If body A and body B are in thermal equilibrium and body B and body C are in thermal equilibrium then body A and body C are in thermal equilibrium

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2
Q

What is the first law of thermal dynamics?

A 
delta U = Q + W 
where :
delta U is the change in internal energy 
Q is the heat energy of a system 
W is the work done on/by the system
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3
Q

Describe the Leonard Jones potential curve

A
  • The Leonard Jones potential curve shows the energy of a atom with respect to the atomic separation.
  • It kind of looks like a inverted bell shape withe an extended tail to the right
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4
Q

What equation and principle of physics explains the scenario where we apply a force F to a bar of area A and of tension-less length L that stretches a length Delta L?

A
  • We are talking about the modulus of elasticity (denoted E)

- This is given by F/A=E.(deltaL/L)

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5
Q

Describe the linear expansion of a solid and its equation

A

When an object is at length L0 and temperature T , and experiences a temperature change delta T, and thus a change in length delta L, the linear expansion can be described as
delta L/L = alpha.delta T

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6
Q

What is the equation of the volume expansion of a solid and how does this compare to that of a linear expansion?

A
  • delta V/V = beta.delta T

- The volume constant beta is approximately 3.alpha (the linear constant)

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7
Q

What are the three types of energy transfer?

A
  • Conduction
  • Convection
  • Radiation
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8
Q

What is the Fourier conduction law?

equation for conduction between different materials

A 
dbar Q/dt = -kA dT/dx
where:
dbar Q is an infinitesimal change in heat 
dt is change in time 
k is the thermal conductivity 
A is the area of contact 
dT is the change in temperature 
dx is the change in length

This can also be written as
dbar Q/dt = -kA.(T1-T2)/delta x

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9
Q

What is the equation for conduction between multiple materials ?

A

dbar Q/dt = (T1-T2)/sum(d/k)
where:
d is the thickness of the material
k is the thermal conductivity

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10
Q

What is the difference between Natural convection and forced convection ?

A
  • Natural Convection is due to differences in densities under gravitational effects
  • Forced Convection is using pumps or fans to move the mass
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11
Q

Describe the mechanism of thermal radiation

A

Heat transfer through emission and absorption of thermal electromagnetic radiation

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12
Q

What is the equation for emission and absorption of an object ?

A

p(emit)=sigmaepsilonA*T^4

p(abs)=sigmaepsilonA*T(env)^4

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13
Q

When are P(abs) and P(emit) equal to one another and what is this called ?

A

P(abs)=P(emit) when epsilon =1

This is known as blackbody radiation

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14
Q

What is the ideal gas law?

A

PV=nRT

PV=NKbT

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15
Q

Describe what is meant by an equation of state

A

An equation of state is when the function of the state only depends on what state that system is in, and not how it arrived at that state

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16
Q

what is the Vrms equation ?

A

sqrt(3KbT/m)

17
Q

What is the definition of the internal energy of a substance and what is its equation ?

A
  • Internal energy is the sum of all the energies stored in the substance. This includes kinetic, potential, mass and chemical energy
  • U=(f/2)NKbT
18
Q

What does the equation lambda = V/(sqrt(2)NPid^2) and what does this actually mean?

A
  • Mean free path equation

- The mean free path equation describes the average distance travelled by a particle in a gas between collisions

19
Q

On a Maxwell-Boltzmann speed distribution graph, what order would the most average, most probable and RMS velocities appear (from left to right)

A

Most probable - Most average - RMS

20
Q

In what scenario does dbar W = -PdV hold?

A

This only holds for reversible reactions

And if dbarQ =0, delta U = -PdV

21
Q

True or False :

Work is a function of state

A

False

22
Q

What is the difference between adiabatic and isothermal reactions ?

A
  • Adiabatic , Q=0

- Isothermal, deltaT = 0

23
Q

What are some of the equations for heat capacity ?

A
  • C=dbarQ/dT
  • Q=C.deltaT
  • c=C/m
24
Q

In thermal physics, what is the gamma factor?

A
  • The gamma factor is the ratio of heat capacity with constant pressure compared to the heat capacity with constant volume
  • gamma =Cp/Cv=1+2/f
25
Q

What is latent heat?

A
  • Adding energy to a system, having no temperature change, but having a change of state of the substance
  • L=Q/m
26
Q

What are some of the reversible reaction equations with respect to P, T, V, gamma and f?

A
  • P1V1^gamma=P2V2^gamma

- T1V1^(2/f)=T2V2^(2/f)

27
Q

True or False:

A set of bulk parameters define the macrostate of a system

A

True

28
Q

What is the definition of multiplicity ?

A

The number of microstates consistent with the number of macrostates is known as the multiplicity

29
Q

What is a fundamental postulate of statistical physics ?

A

All accessible microstates are equally probable

30
Q

True or False:

a system left to itself will evolve to the macrostate with the lowest multiplicity

A

False

-It will evolve to one of the highest multiplicity

31
Q

What is the equation for entropy?

A

S=Kb.ln(omega)

dS=dbarQ/dT

32
Q

What is the second law of thermodynamics ?

A

The entropy of any system is greater than or equal to zero, never smaller than zero.

33
Q

What is the Thermodynamic identity and name the types of reactions this identity applies too

A

dU=TdS-PdV

This applies to both reversible and irreversible processes

34
Q

What is the link between entropy and reversibility of a process?

A

A process is reversible if it does not increase the entropy of the system it is in or the universe as a whole

35
Q

What are the 4 processes in the Carnot cycle (reversible) for heat engines ?

A
  • Isothermal expansion
  • Adiabatic expansion
  • Isothermal compression
  • Adiabatic compression
36
Q

What is efficiency in regards to heat engines and what are the equations for this ?

A

-Efficiency is a ration of useful word to the heat from a hot reservoir in a heat engine
-E= -W(cycle)/Qh
-E=1-Tc/Th
where:
Tc is temp of cold reservoir
Th is temp of hot reservoir

37
Q

What is the coefficient of performance of a refrigerator ?

A

k=Tc/Th-Tc

Physics 2A (4 decks)

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