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

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.

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

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  1oC = 1.8oF

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

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

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

http://www.astronomynotes.com/light/s2.htm

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

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

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

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

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

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

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

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

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

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

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

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

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

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.)

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

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

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

Wavelength (m)