1. Physics 2
Chapter 10
Sections 1 - 4

2. PV = NkbT P = pressure Ideal Gas Law V = volume
T = temperature in Kelvin
N = number of gas molecules
kb = Boltzmann’s constant = 1.38 x J/K
Pressure of a gas can be changed in several ways: if constant volume could increase number of molecules, for any gas could change temp or volume
No gas obeys the ideal gas law exactly for all temps and pressures
At relatively high temps and low pressures (room temp & atm pressure) real gases follow pretty closely

3. Ideal Gas Law
PV = NkbT is the microscopic form of the ideal gas law - refers specifically to the number of molecules PV = nRT is the macroscopic form of the ideal gas law - involves quantities that can be measured with everyday lab equipment - n refers to the number of moles of the gas - R = 8.31 J/(mol * K)

4. Temperature
Is proportional to the average kinetic energy of molecules on a substance.
As substances increase temperature their molecules increase speed and KE.
Every substance has a rate of increase of temperature that relates to the average KE of its molecules, this is its specific heat constant.
Metals typically have very low spefic heats meaning they don’t require much energy to warm or cool.

5. Temperature Thermometer – 1st invented by Galileo
- uses the fact that materials
usually expand when temp
increases. This is because as molecules increase velocity they
occupy more space.

6. Temperature cont’d. Temperature scales:
Celsius or centigrade- Based on the freezing and boiling point of water.
0- FP BP
Fahrenheit- Based on the highest FP and BP temperature with added impurities
32- FP BP
Kelvin- Based on Absolute Zero
FP BP

7. Temperature cont’d.
Celsius and Fahrenheit scales were developed by arbitrarily assigning a number to boiling and freezing points and then dividing the range into equal intervals
Celsius – boiling point 100 °C
freezing point 0 °C
Fahrenheit – boiling point 212 °F
freezing point 32 °F
Tf = /5 Tc

8. Temperature cont’d.
Kelvin scale was introduced by Scottish physicist William Thomson (Lord Kelvin)
Kelvin, K is the standard for temperature scales
Kelvin – boiling point K
freezing point K
absolute zero 0 K
(note not °K)
TK = TC

9. Linear Expansion Increase in any one dimension of a solid when heated
Linear expansion of a solid depends on temp change
greater ΔT……. greater ΔL
For modest ΔT, ΔL α ΔT
ΔL α L0
Consider 2 identical rods of length L that each expand ΔL
Total expansion of 2 rods “put together” is 2 ΔL for 2L

10. Linear Expansion cont’d.
ΔL = α L ΔT
α = coefficient of linear expansion
L = original length
ΔT = change in temperature in Celsius
[α] = 1/C°
Different materials will have different α values

11. Linear Expansion cont’d.
Sample problem #1 h = m
Usually provide expansion joints or spaces for bridges, railroad tracks If

12. Bimetallic Strip
Strip made from 2 thin strips of metal that have different coefficients of linear expansion
Often brass and steel
brass α = 1.9 x /C°
steel α = 1.2 x /C°
Since brass has higher coeff is expands more which bends the strip into arc toward steel
Used in automatic switches in electrical appliances

13. Volume Expansion
Increase in all dimensions of a material as the temperature increases
volume expansion of a solid depends on temp change
greater ΔT……. greater ΔV
For modest ΔT, ΔV α ΔT
ΔV α V0

14. Volume Expansion cont’d.
ΔV = β V ΔT
β = coefficient of volume expansion
V = original volume
ΔT = change in temperature in Celsius
[β] = 1/C°
Different materials will have different β values

15. Volume Expansion cont’d.
H β = 2.1 x /C°
β is much larger for liquids than solids
For most solids β = 3 α
If a cavity exists in a solid the volume of the cavity increases when object expands
Sample Problem # qts.

16. Volume Expansion cont’d.
Some substances are weird and don’t expand when heated
Ex - H20
if heated from 0 °C to 4 °C its volume
decreases
above 4 °C its volume increases like normal
this happens because water has greatest
density at 4 °C