PHYS-307 Midterm Questions With 100% Correct Answers 2024/2025
9 keer bekeken 0 keer verkocht
Vak
PHYS-307
Instelling
Arizona State University
PHYS-307 Midterm Questions With 100% Correct Answers 2024/2025
Energy as a function of quantum number - ANS-= -13.6 eV (Z²/n²)
lifetime of an orbit/time to decay to lower energy level - ANS-t = E/(dE/dt) = E_n/P
= 4.7x10^-11 s (h⁶/Z⁴)
energy difference between two states, n1 and n2: - AN...
relation between kinetic energy and thermal energy of a particle - ANS-✔✔1/2 mv² = kT
,What is the maximum of the Maxwell-Boltzmann distribution, and how do we find it? What does it
represent? - ANS-✔✔v_p = (2kT/m)^1/2
It represents the most probable speed for a particle
average speed of a particle - ANS-✔✔<v> = 1.6 (kT/m)^1/2
mean kinetic energy per particle: - ANS-✔✔<E> = 3/2 kT
Rotational Broadening - ANS-✔✔seen in rapidly rotating objects
Which three types of broadening are all very general Doppler-based motion/line-of-sight effects? - ANS-
✔✔thermal, turbulent, and rotational broadening
optical depth - ANS-✔✔a measure of how much the intensity of light is attenuated by traveling through
the gas
T(x) = σN(x)
if N is constant:
T(x) = σnx
optically thin - ANS-✔✔T(x) << 1
σnx << 1
optically thick - ANS-✔✔T(x) >> 1
σnx >> 1
,mean free path (mfp) - ANS-✔✔average distance a photon will travel through a gas before being
absorbed
-for a gas with constant n and σ:
<x> = 1/nσ
mfp is the distance over which the optical depth grows from T=0 to T=1
Curve of growth:
Describe line and profile anatomy at low optical depth T₀<1 - ANS-✔✔the shape and width of the
absorption line is determined by thermal Doppler broadening
-Gaussian shape, width depends on temperature and molecular mass of absorbing particles. the wings
are weak
Curve of growth:
Describe line and profile anatomy at larger optical depth, 1<T₀<10⁴ - ANS-✔✔the line core saturates,
the line is black at the center because none of the photons with a wavelength enar the line center make
it through the absorbing gas. the width of the line only grows slowly with optical depth
Curve of growth:
Describe line and profile anatomy at very large optical depth, T₀>10⁴ - ANS-✔✔the cumulative effects
of the (v-v₀)² wings of the Lorentz profile are important. the column density of atoms is now so large
that photons far from the center (|v-v₀|>>γ) have a fair probability at being absorbed
-even at low resolution, absorption lines are easily detected and measured
equivalent width - ANS-✔✔width of a rectangle from continuum to zero with the same area as a line;
use FWHM or triangle approximation
W = ∫(I_cont-I_line)/I_cont dλ = ∫[1-e^(-Tλ)]dλ
, curve of growth - ANS-✔✔a plot of an absorption line's equivalent width W as a function of T₀ (or a
function of column density N of the absorbing atoms) with 3 parts
Local Thermodynamic Equilibrium - ANS-✔✔all particles characterized by the same temperature T,
where:
½mv² = (3/2)kT;
all molecules have frequent collisions, so they all have the same average kinetic energy and temperature
What do we need to achieve LTE with photons? - ANS-✔✔1. a high number density of photons and
massive particles (nuclei)
2. optically thick at all wavelengths- otherwise particles, photons are decoupled
What does the Boltzmann equation tell us? - ANS-✔✔gives the relationship between the number of
atoms in one excitation state to another, e.g., n₂/n₁, and allows us to relate what we see in spectral lines
to the physical conditions of the gas
Trends for a fixed E_B and E_A, and for a fixed T in the Boltzmann equation - ANS-✔✔1. As T → ∞,
N_B/N_A → g_B/g_A
2. As T → 0 , N_B/N_A → 0
When T is fixed:
1. As E_B increases, or E_A-E_B→∞, N_B/N_A→0
2. as E_A-E_B → -kT, N_B/N_A → e-¹
3. As E_A-E_B → 0 , N_B/N_A → g_B/g_A
What is different between the Saha and Boltzmann equations? - ANS-✔✔electron density dependence
Voordelen van het kopen van samenvattingen bij Stuvia op een rij:
Verzekerd van kwaliteit door reviews
Stuvia-klanten hebben meer dan 700.000 samenvattingen beoordeeld. Zo weet je zeker dat je de beste documenten koopt!
Snel en makkelijk kopen
Je betaalt supersnel en eenmalig met iDeal, creditcard of Stuvia-tegoed voor de samenvatting. Zonder lidmaatschap.
Focus op de essentie
Samenvattingen worden geschreven voor en door anderen. Daarom zijn de samenvattingen altijd betrouwbaar en actueel. Zo kom je snel tot de kern!
Veelgestelde vragen
Wat krijg ik als ik dit document koop?
Je krijgt een PDF, die direct beschikbaar is na je aankoop. Het gekochte document is altijd, overal en oneindig toegankelijk via je profiel.
Tevredenheidsgarantie: hoe werkt dat?
Onze tevredenheidsgarantie zorgt ervoor dat je altijd een studiedocument vindt dat goed bij je past. Je vult een formulier in en onze klantenservice regelt de rest.
Van wie koop ik deze samenvatting?
Stuvia is een marktplaats, je koop dit document dus niet van ons, maar van verkoper Accurate. Stuvia faciliteert de betaling aan de verkoper.
Zit ik meteen vast aan een abonnement?
Nee, je koopt alleen deze samenvatting voor €14,63. Je zit daarna nergens aan vast.
