Kelvin Scale

1
Kelvin Scale

• Absolute temperature

17.3
2
Temperature and Gas Pressure
(constant volume)
Source Griffith, Physics of Everyday Phenomena,
Fig. 10.6
3
Absolute Zero

• Gas p decreases with T

• Absolute zero ? T at which p 0
• Minimum total molecular kinetic energy

4
Kelvin scale

• Unit K
• K same size as C
• but
• 0 K absolute zero
• (T in K) 273.15 (T in C)

5
CPS Question

• How do the temperatures 273.25 C and 273.15 K
  compare?
• 273.15 C is the same as 273.15 K.
• 273.15 C is half 273.15 K.
• 273.15 C is twice 273.15 K.
• 273.15 C is absolute zero.

6
Thermal Expansion

• size does matter

17.4
7
Linear Expansion

• a coefficient of linear expansion
• valid for small DT

8
CPS Question

• A metal ring is heated. What happens to its
  outer diameter?
• It increases.
• It stays the same.
• It decreases.
• Impossible to determine.

9
CPS Question

• A metal ring is heated. What happens to its
  inner diameter?
• It increases.
• It stays the same.
• It decreases.
• Impossible to determine.

10
Volume Expansion

• If expansion is isotropic,
• and DT is small,
• b 3a

11

• V0 L0x L0y L0z
• V V0 DV (L0x L0xaDT) (L0y L0yaDT) (L0y
  L0yaDT)
• L0x L0y L0z (1 aDT)3
• L0x L0y L0z (1 aDT)3
• 1 DV/V0 1 3aDT 3a2DT2 DT3
• DV/V0 ? 3aDT
• Q.E.D.

12
Water is Weird
Source Young and Freedman, Figure 17.12

• Density maximum disappears above 2.5 salt

13
CPS Question

• Between 0 C and 4 C, warmer fresh water
• Rises above colder water.
• Sinks beneath colder water.
• Has neutral buoyancy.
• It is impossible to determine.

14
Thermal Stress

• Results from

• Uneven composition
• Uneven temperature