Physics 2

1
Physics 2

• Chapter 10
• Sections 1 - 4

2
Ideal Gas Law

• PV NkbT
• P pressure
• V volume
• T temperature in Kelvin
• N number of gas molecules
• kb Boltzmanns constant 1.38 x 10-23 J/K

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

• Degree of hotness or coldness measured on a
  definite scale
• Thermometer 1st invented by Galileo
• - uses the fact that materials
• usually expand when
  temp
• increases

5
Temperature contd.

• Temperature scales
• Celsius (used to be called centigrade)
• Fahrenheit
• Kelvin

6
Temperature contd.

• 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 32 9/5 Tc

7
Temperature contd.

• Kelvin scale was introduced by Scottish physicist
  William Thompson (Lord Kelvin)
• Kelvin, K is the standard for temperature scales
• Kelvin boiling point 373.15 K
• freezing point 273.15 K
• absolute zero 0 K
• (note not K)
• TK TC 273. 15

8
Linear Expansion

• Increase in any one dimension of a solid when
  heated
• Linear expansion of a solid depends on temp
  change
• greater ?T. greater ?L
• For modest ?T, ?L a ?T
• ?L a L0

9
Linear Expansion contd.

• ?L a L ?T
• a coefficient of linear expansion
• L original length
• ?T change in temperature in Celsius
• a 1/C
• Different materials will have different a values

10
Linear Expansion contd.
11
Bimetallic Strip

• Strip made from 2 thin strips of metal that have
  different coefficients of linear expansion
• Often brass and steel
• brass a 1.9 x 10-5 1/C
• steel a 1.2 x 10-5 1/C
• Since brass has higher coeff is expands more
  which bends the strip into arc toward steel
• Used in automatic switches in electrical
  appliances

12
Volume Expansion

• Increase in all dimensions of a material as the
  temperature increases
• volume expansion of a solid depends on temp
  change
• greater ?T. greater ?V
• For modest ?T, ?V a ?T
• ?V a V0

13
Volume Expansion contd.

• ?V ß V ?T
• ß coefficient of volume expansion
• V original volume
• ?T change in temperature in Celsius
• ß 1/C
• Different materials will have different ß values

14
Volume Expansion contd.

• H20 ß 2.1 x 10-4 1/C
• ß is much larger for liquids than solids
• For most solids ß 3 a
• If a cavity exists in a solid the volume of the
  cavity increases when object expands

15
Volume Expansion contd.

• Some substances are weird and dont 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