In Antarctica the thermometer reads

1
In Antarctica the thermometer reads 20 C what
is this temperature on a Fahrenheit thermometer?
Physics 1710Warm-up Quiz

0

1. -36 oF
2. -11 oF
3. -4 oF
4. -43 oF
5. -20 oF

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Physics 1710 Chapter 20 Heat 1st Law of Thermo
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• Solution
• oF (180 oF/100 oC) oC 32oF
• (1.8 oF/oC)(-20 oC) 32oF
• (-36 32) oF
• -4oF

3
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0
What will happen to a heated ring? The hole
will(1) get larger (2) get smaller (3) stay
the same.
Peer Instruction Time
4
What will happen to a heated ring? The hole will
Physics 1710 e-Quiz

0

1. Get larger
2. Get smaller
3. Stay the same

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5
Physics 1710 Chapter 20 Heat 1st Law of Thermo
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• Time for Real Physics!

6
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• Why did it happen?

?L
?L
?L a L?T
7
Physics 1710Chapter 19 Temperature
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• Ideal Gas Law
• Idealizations
• no interaction between atoms
• no volume occupied by atoms
• Number of atoms n m/M,
• m mass M molar mass
• PV n R T
• R 8.315 J/ mol K
• 0.08214 L?atm/mol K
• 22.4 L?atm /273.16 mol K

8
Physics 1710Chapter 19 Temperature
0

• Boltzmann Constant
• k R/NA
• k 1.38 x 10 -23 J/K 1 yJ/ 7.25 K
• 1 eV / 11,600 K
• PV N kT

9
Physics 1710Chapter 19 Temperature
0

• Summary
• Temperature is a measure of the average kinetic
  energy of a system of particles.
• Thermal Equilibrium means that two bodies are at
  the same temperature.
• The Zeroth Law of Thermodynamics states that
  if system A and B are n thermal equilibrium with
  system C, then A and B are in thermal Equilibrium
  with each other.

10
Physics 1710Chapter 19 Temperature
0

• Kelvin is a unit of temperature where one degree
  K is 1/279.16 of the temperature of the triple
  point of water (near freezing).
• TC (100/180) (TF 32 F)
• TF (180/100) TC 32 F
• ?L/L a?T
• PV n R T N kT

11
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• 1' Lecture
• The internal energy is the total average energy
  of the atoms of an object, average kinetic plus
  average potential.
• Heat is the change in internal energy.
• The change in temperature is proportional to the
  change in internal energy (heat flow) when there
  is no change of phase and the system does no
  work.
• The first law of thermodynamics states
• ?E ?Q - W

12
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• 1' Lecture
• Conduction is the flow of kinetic energy from
  atom to atom.
• Convection is the transport of energy by bulk
  motion of atoms.
• Radiation is the transfer of energy by
  electromagnetic waves.

13
Physics 1710 Chapter 20 Heat 1st Law of Thermo
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• Heat
• Heat is the macroscopic manifestation of
  microscopic internal energy.
• Heat ?Q in calories (or BTU)
• 1 calorie (cal) is the amount of energy required
  to raise the temperature of 0.001 kg of water
  from 14.5 C to 15.5 C (?T 1.00 C).
• 1 BTU is the heat to raise 1 Lb by 1 F.
• James Prescott Joule (1818-1889) showed
• 1 calorie of heat 4.186 Joule
• 1 J 1 N?m

14
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• 1 Calorie 1000 calorie 1 kcal

15
Physics 1710 Chapter 20 Heat 1st Law of Thermo
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• Heat Capacity
• ?Q C ?T
• C dQ/dT
• Specific Heat
• c C /m
• C (1/m)dQ/dT
• ?Q (mc)?T

16
How much heat is required to raise the
temperature of 1 kg of water (1 liter) from 20 C
to 100 C? Recall c 1.00 kcal/kgC?
Physics 1710 e-Quiz

0

1. 1.0 kcal
2. 20 kcal
3. 80 kcal
4. 100 kcal
5. None of the above.

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17
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• Guided practice
• ?Q (mc)?T
• How much heat is required to raise the
  temperature of 1 kg of water (1 liter) from 20 C
  to 100 C? Recall c 1.00 kcal/kgC?

?Q (mc)?T ?Q (1.00 kg)(1.00 kcal/kg C) (100.
C- 20. C) ?Q 80. kcal 80.kcal? 4.186 J/cal
396. kJ
18
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• Change of Phase and Latent Heat
• It requires an energy investment to change the
  phase from solid to liquid to gas.
• By breaking the bonds that hold atoms, they can
  have the same kinetic energy but different total
  energies.
• The energy to change the phase is hidden and
  therefore called latent heat.

19
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• Latent heat
• ?Q mL
• For Water
• Fusion (and melting)
• Lf 333 kJ/kg 79.4 kcal/kg
• Vaporization
• Lv 2260 kJ/kg 540 kcal/kg

20
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• Work from a Heat Reservoir
• The work done by a system is equal to the loss
  of the internal energy.
• For an ideal gas
• W ?V1V2 PdV

21
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• First Law of Thermodynamics
• ?E ?Q -W

22
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• ApplicationsAdiabatic (?Q 0)
• ?E -W
• Isovolumetric (?V 0)
• ?E ?Q
• Isothermal (?T 0)
• W ?V1V2 PdV ?V iV f (nRT/V) dVW n R T
  ln(Vf /Vi )

23
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• Mid Chapter Summary
• The internal energy is the total average energy
  of the atoms of an object.
• Heat is the change in internal energy.
• The change in temperature is proportional to the
  change in internal energy (heat flow) when there
  is no change of phase and the system does no
  work.
• The first law of thermodynamics states
• ?E ?Q - W

24
Physics 1710 Chapter 20 Heat 1st Law of Thermo
0

• Conduction
• P kA dT/dx
• Examples
• Thermos bottles
• Blankets
• Double pane windows
• Newtons law of cooling P h A(T 2 T1)
• Pans
• R factor or R value
• P A(T 2 T1)/?i Ri

25
Physics 1710 Chapter 20 Heat 1st Law of Thermo

• Convection
• Heat transfer by material transfer
• Forced convection (fluids)
• External force produces material transfer
• Natural Convection
• Buoyancy-driven flow
• Newtons law of cooling applied
• P h A(T 2 T1)
• h depends on flow conditions

26
Physics 1710 Chapter 20 Heat 1st Law of Thermo

• Radiation
• Stefan-Boltzmann Law
• P es AT4
• Wiens Law
• P ?T4
• s 5.6696 x 10-8 W/m2?K4
• Emissivity 0lt e lt1 e ½
• Reflectivity (albedo) R (1- e)
• Energy balance
• P in - es A(Tave ) 4 0

27
Physics 1710 Chapter 20 Heat 1st Law of Thermo

• Global Warming?
• P in ( 1- e?) Psun
• Tave ( 1- e?) Psun /(eGH sA)1/4
• Must understand every parameter
• to be accurate.

28
Physics 1710 Chapter 20 Heat 1st Law of Thermo

• Summary
• Heat is transferred by
• Conductionenergy diffusion
• Convectionmass transport
• Radiationelectromagnetic waves

29
Physics 1710 Chapter 20 Heat 1st Law of Thermo

• Guided Practice
• If the power per unit area (intensity) of
  sunlight on the earth is 1.0 kW/m2 and the
  emissivity is 0.6, what is the expected avearge
  temperatue of the earth? Comment on the effect
  of a change in the emissivity or solar
  radiation.

P in ?0 2p?0 p/2 I cos ? sin ? r 2d? df P in I
(2pr 2) (½ ) sin2 ? 0 p/2 I (pr 2) 1.0
kW/m2 (3.14)(6.4x106 m)2 1.3 x 1017 W P in es
A(Tave ) 4 Tave P in / es A1/4 1.3 x
1017 /(0.6?5.66 x10-8? 5.1x1014) 1/4 294 K21C
30
Physics 1710 Chapter 20 Heat 1st Law of Thermo

• Guided Practice
• If the power per unit area (intensity) of
  sunlight on the earth is 1.0 kW/m2 and the
  emissivity is 0.6, what is the expected average
  temperature of the earth? Comment on the effect
  of a change in the emissivity or solar radiation.