1. The Mechanisms of Electromagnetic Emissions
GAVRT Chapter 3
With a Review of Thermodynamics

2. Temperature, Heat and Internal Energy
Temperature is measurement of average speed of particles inside a substance. The faster the motion of the particles the greater the temperature.
Internal or thermal energy includes the energy of the motion of atoms and molecules inside a substance
Heat is thermal energy in motion. Like work it is an energy transfer device
Heat flows from a hot object to a cool one until the temperatures of both objects are the same.
Temperature does not depend on the number of particles whereas internal energy does. Sparkler analogy

3. First Law of Thermodynamics
First Law of Thermo DU=Q-W
Restatement of conservation of energy
No such thing as 100% efficient heat engine
Carnot Efficiency =Max Efficiency = (T hot-T cold) / T hot
Assumes no friction

4. Second Law of Thermodynamics
Heat tends to flow from hot to cold.
Entropy of a system tends to increase with time
Probability statements so can never be broken

5. Blackbody Radiation
Blackbody radiation is emitted by any matter with a temperature above absolute zero
Blackbody model assumes energy at all frequencies is absorbed and re-emitted. No reflection occurs.
Type of thermal emission

6. Blackbody Brightness Curves
Flux density = brightness = energy/unit area/ 1 hz of frequency measured in Janskys
Frequency increases to right, wavelength to left
As temperature of black body increases
Total energy at each wavelength increases (Energy ~ T4)
Wavelength of maximum emission decreases (Wein’s Law, E=hf)
Curves do not cross meaning that can tell temperature of object with one data point
Brightness Curves
We have a way to find the temperature of a body simply by looking at its brightness curve. Does not work for stars but does for planets like JUPITER

7. Other Thermal Radiation Means
Continuous Emissions from Plasmas
Range of frequencies emitted as electrons and ions recombine
Plasma is high temp phase w/ separate charges
Spectral Line Emissions from atoms and molecules
Single frequencies emitted
Neutral Hydrogen 21.1 cm emission of Jansky (H 1 region)
H 2 Region=ionized gas around new stars

8. Synchrotron Radiation
Non-thermal radiation
Electric particles feel force when moving in magnetic field
Force is perpendicular to both direction of particles motion and magnetic field
Force provides centripetal acceleration causing particle to spiral around magnetic field line and emit radio signal
Examples
Picture of electron spiraling around magnetic field line

9. MASERs Microwave amplified stimulated emission of radiation
Non-thermal radiation source
Intense radiation field pumps molecules of cloud so emit at same time.
Emission is at single frequency akin to spectral line emission frequency

10. Thermal vs Non-Thermal Radiation Sources
Thermal radiation sources have their intensity increase with receiving frequency
Non-thermal radiation sources have their intensity decrease with receiving frequency
Review of radiation sources
Curve on page 27

11. Blackbody Radiation Thermal radiation source
Black body is object that absorbs energy and emits energy at all frequencies of radiation without reflection
Heat is first absorbed by object and then radiated at all frequencies by motion of charged particles within object
Temperature determines intensity and spectrum of emissions from body
Black body puts out energy at all frequencies
Higher frequencies have greater energy/photon (Planck’s law E=hf)
All matter in the universe behaves as a black body when heated
Brightness Curve pictures and use to explain how can get temperature of Jupiter