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

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

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

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

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

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

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

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

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

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

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