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Thermodynamics > THERMO1 > Flashcards

THERMO1 Flashcards

1
Q

0th Law of Thermodynamics

A

Defines temperature

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2
Q

1st Law of Thermodynamics

A

Conservation of energy

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3
Q

2nd Law of Thermodynamics

A

The entropy of an isolated system can never decrease

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4
Q

3rd Law of Thermodynamics

A

The entropy of a perfect crystal tends to zero at absolute zero

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5
Q

Zeroth Law of Thermodynamics

A

If two objects are in thermal equilibrium with a third, then the two objects are also on thermal equilibrium with each other

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6
Q

What is thermal equilibrium?

A

When heat flow ceases

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7
Q

What is heat?

A

Flow of energy caused by a difference in temperature

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8
Q

What is temperature?

A

A measure of the average translational kinetic energy per molecule

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9
Q

What happens when an object absorbs heat?

A

It increases its internal energy

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10
Q

What is a thermal reservoir?

A

An object with such a large specific heat capacity that any transfer of heat will not change its temperature

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11
Q

What does the amount of heat flow depend on?

A

Mass
Specific heat capacity
Temperature difference

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12
Q

Bose-Einstein Condensate

A

When the de Broglie wavelength of atoms becomes bigger than the atomic spacing
Occurs when a solid is cooled to a very low temperature

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13
Q

Cooling to Lower than the Surroundings

Magnetic Cooling

A
  • atoms with magnetic dipoles can be aligned with a magnetic field
  • if the magnetic field is slowly decreased then the dipoles can overcome the field and become randomly orientated by taking thermal energy from their motion
  • this leads to sample cooling as the average translational kinetic energy per molecule is decreasing
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14
Q

Cooling to Lower than the Surroundings

Laser Cooling

A
  • a laser photon of momentum p = hf is fired at the sample
  • the frequency of each photon is slightly less than the frequency corresponding to the transition energy of the atoms
  • this means that it can only be absorbed by atoms travelling towards it by the Doppler shift effect
  • this collision reduces the velocity of the atom
  • average kinetic energy and therefore temperature are reduced
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15
Q

Cooling to Lower than the Surroundings

Evaporative Cooling

A
  • atoms are held in a magnetic trap
  • only atoms with the highest velocity are able to escape
  • as these high energy atoms leave the average kinetic energy of the atoms in the magnetic trap decreases
  • the magnetic field is decreased so that atoms can continue to escape
  • this continues until there are far fewer but much colder atoms remaining
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16
Q

What kinetic energy do atoms have at absolute zero?

A

Zero translational kinetic energy

17
Q

What is the lowest temperature ever achieved?

A

100pK

18
Q

Cooling to Absolute Zero

A
  • removing all possible energy would require an infinite amount of time
  • it would contradict the Heisenberg Uncertainty Principle which doesn’t allow no motion as then it would be possible to specify both position and momentum precisely
  • zero-point energy remains
19
Q

Thermal Expansion

Linear Expansion

A

ΔL = LαΔT

L = initial length 
α = coefficient of linear expansion
20
Q

Coefficient of Linear Expansion

A

α = (ΔT->0)lim 1/L * dL/dT

21
Q

Thermal Expansion

Volume Expansion

A

ΔV = VβΔT

V = initial volume
β = coefficient of volume expansion
22
Q

What is the relationship between the coefficient of linear expansion and the coefficient of volume expansion?

A

β = 3α

23
Q

At what temperature does water have maximum density?

A

4°C

24
Q

Thermal Current

A

I = ΔQ/Δt = kA * ΔT/Δx

25
Q

Thermal Conduction

V=IR

A

ΔT = IR = I*Δx/kA

26
Q

Thermal Resistance

A

R = ΔX/kA

27
Q

Thermal Resistors

Series

A

Rt = R1 + R2 + R3 + …

E.g. double glazing

28
Q

Thermal Resistors

Parallel

A

1/Rt = 1/R1 + 1/R2 + 1/R3 + …

29
Q

What is convection?

A

The transfer of thermal energy by direct mass transport

30
Q

What is radiation?

A

The transfer of thermal energy in the form of electromagnetic radiation
No medium is necessary

31
Q

Stefan-Boltzmann Law

A

Pnet = eσA (T⁴ - T0⁴)

32
Q

Wien’s Displacement Law

A

λmax = 2.898mmK / T

Thermodynamics (7 decks)

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