Flashcards in THERMO1 Deck (32):

1

## 0th Law of Thermodynamics

### Defines temperature

2

## 1st Law of Thermodynamics

### Conservation of energy

3

## 2nd Law of Thermodynamics

### The entropy of an isolated system can never decrease

4

## 3rd Law of Thermodynamics

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

5

## Zeroth Law of Thermodynamics

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

6

## What is thermal equilibrium?

### When heat flow ceases

7

## What is heat?

### Flow of energy caused by a difference in temperature

8

## What is temperature?

### A measure of the average translational kinetic energy per molecule

9

## What happens when an object absorbs heat?

### It increases its internal energy

10

## What is a thermal reservoir?

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

11

## What does the amount of heat flow depend on?

###
Mass

Specific heat capacity

Temperature difference

12

## Bose-Einstein Condensate

###
When the de Broglie wavelength of atoms becomes bigger than the atomic spacing

Occurs when a solid is cooled to a very low temperature

13

##
Cooling to Lower than the Surroundings

Magnetic Cooling

###
-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

14

##
Cooling to Lower than the Surroundings

Laser Cooling

###
-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

15

##
Cooling to Lower than the Surroundings

Evaporative Cooling

###
-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

16

## What kinetic energy do atoms have at absolute zero?

### Zero translational kinetic energy

17

## What is the lowest temperature ever achieved?

### 100pK

18

## Cooling to Absolute Zero

###
-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

##
Thermal Expansion

Linear Expansion

###
ΔL = LαΔT

L = initial length

α = coefficient of linear expansion

20

## Coefficient of Linear Expansion

### α = (ΔT->0)lim 1/L * dL/dT

21

##
Thermal Expansion

Volume Expansion

###
ΔV = VβΔT

V = initial volume

β = coefficient of volume expansion

22

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

### β = 3α

23

## At what temperature does water have maximum density?

### 4°C

24

## Thermal Current

### I = ΔQ/Δt = kA * ΔT/Δx

25

##
Thermal Conduction

V=IR

### ΔT = IR = I*Δx/kA

26

## Thermal Resistance

### R = ΔX/kA

27

##
Thermal Resistors

Series

###
Rt = R1 + R2 + R3 + ...

E.g. double glazing

28

##
Thermal Resistors

Parallel

### 1/Rt = 1/R1 + 1/R2 + 1/R3 + ...

29

## What is convection?

### The transfer of thermal energy by direct mass transport

30

## What is radiation?

###
The transfer of thermal energy in the form of electromagnetic radiation

No medium is necessary

31

## Stefan-Boltzmann Law

### Pnet = eσA (T⁴ - T0⁴)

32