1. Principles of Heat and Radiation
Chapter 3—Part 1
Principles of Heat
and Radiation

2. Thermal Energy
All matter is composed of atoms or molecules, which are in constant motion
Molecular or atomic motion = “thermal energy”
Heating atoms causes them to move faster, which represents an increase in thermal energy.
Temperature is a measure of thermal energy.

3. a measure of the average motion of atoms or molecules
Temperature:
a measure of the average motion of atoms or molecules

4. scale
melting point of ice
boiling point of water
Fahrenheit (oF) 32
212
Celsius
(oC)
100
Kelvin
(K)
273
373
Relative size of a degree F vs. a degree C--compare
the number of degrees between freezing and boiling:
100oC = 180oF
 oC = 1.8oF

5. Fahrenheit and Celsius
Temperature Scales:
Fahrenheit and Celsius
(oC x 1.8) + 32 = oF
(oF - 32) / 1.8 = oC
(see appendix B in text)

6. Question: How does energy flow?
(Hint: There are 3 different mechanisms)
Conduction
Convection
Radiation

7. Radiation Energy is transferred by electromagnetic waves
This includes all radiant energy:
X-rays
Radio waves
Light (sunlight)
Microwaves

9. Properties of Waves All electromagnetic waves travel at the same speed
The speed of light: 300,000 km/s
crest
trough

10. Properties of Waves Wavelength (): the length of one complete cycle
(length/cycle)
crest
trough
Wavelength (): the length of one complete cycle

11. Properties of Waves Amplitude: 1/2 height between trough and crest
Wavelength
(length/cycle)
crest
Amplitude
trough
Amplitude: 1/2 height between trough and crest

12. Properties of Waves Frequency (): the number of cycles/second
Wavelength
(length/cycle)
crest
Amplitude
trough
Frequency (): the number of cycles/second

13. c =   Speed = wavelength x frequency
(length/second) = (length/cycle) x (cycle/second)
Hence,  = c / 
and  = c / 

14. Energy of a wave E = h  = h (c/ )
Energy is proportional to frequency,
and inversely proportional to wavelength
E = h 
= h (c/ )
where h = Planck’s constant
In other words, waves with shorter wavelengths
(or higher frequency) have higher energy

15. Electromagnetic Spectrum
1000
100 10 1
0.1
0.01
 (m)
( = “micro” = 10−6)

16. Electromagnetic Spectrum
visible
light
1000
100 10 1
0.1
0.01
0.7 to 0.4 m
 (m)

17. Electromagnetic Spectrum
visible
light
ultraviolet
1000
100 10 1
0.1
0.01
 (m)

18. Electromagnetic Spectrum
visible
light
infrared
ultraviolet
1000
100 10 1
0.1
0.01
 (m)

19. Electromagnetic Spectrum
visible
light
microwaves
infrared
ultraviolet
x-rays
1000
100 10 1
0.1
0.01
 (m)

20. Electromagnetic Spectrum
visible
light
microwaves
infrared
ultraviolet
x-rays
1000
100 10 1
0.1
0.01
Low
Energy
High
Energy
 (m)

21. Red-Orange-Yellow-Green-Blue-Indigo-Violet
Visible Light (VIS)
0.7 to 0.4 m
Our eyes are sensitive to this region of the spectrum
Red-Orange-Yellow-Green-Blue-Indigo-Violet

22. Infrared Radiation (IR)
We can’t see IR, but we can feel it as radiant heat
Lower energy than visible light
(An image of a human hand, taken in the infrared, and displayed in false color. Here white and yellow correspond to hot regions, blue and green to cool regions.)

23. Ultraviolet Radiation (UV)
Higher energy than visible light
Can burn human skin and damage cells

24. The source for 99.9% of Earth’s energy
Solar Radiation:
The source for 99.9% of Earth’s energy
NASA/ESA SOHO

25. Solar Spectrum The sun emits radiation at all wavelengths
Most of its energy is in the IR-VIS-UV
portions of the spectrum
~50% of the energy is in the visible region
~40% in the near-IR
~10% in the UV

26. Wavelength (m)