Kaplan MCAT Physics Ch. 11: Atomic Phenomena

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sportyperson246  on July 5, 2012

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Kaplan MCAT Physics Ch. 11: Atomic Phenomena

 ideal radiator => blackbodyideal radiator is also ideal absorber and would appear totally black if temp lower that surroundings, since absorb all wavelengths of EM radiation
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ideal radiator => blackbody ideal radiator is also ideal absorber and would appear totally black if temp lower that surroundings, since absorb all wavelengths of EM radiation

blackbody radiator can be approx. to this
Planck's formula for blackbody, one wavelength at which max. amount of energy is emitted (peak)

depends on abs. temp of body in relation to Wien's displacement law

cooler => radiates less energy => other object has higher abs. temp
Wien's displacement law (peak)(T) = constant
(peak) more energy is emitted than at any other wavelengh, but doesn't refer to max. wavelength emitted
Stefan-Boltzmann law total energy emitted per sec per unit area (W/m^2) prop. fourth power of abs. temp

inc. abs temp => inc. intensity => peak wavelength dec.
photoelectric effect light => freq => metal => emit electrons => net charge flow per unit time, or current

all or none response
threshold frequency (fT) min. freq. of light that causes ejection of electrons

depends on type of metal

light quanta (photons) => energy of each prop. to freq. of light

E = hf

h= Planck's constant

high freq => shorter wavelength => higher energy (same for vice versa)

common units = nm and angs
wavelength if know freq, can solve for this

=c/f
c = speed of light
max. KE if freq. of photon on metal at threshold => electrons barely escape

more that enough energy => eject => excess energy converted to KE of ejected

K = hf - W
work function (W) function of min. energy required to eject electron

related to threshold freq of that metal

W = hf(T)
freq. pattern in photoelectric effect freq < thres. freq => no electron ejected

freq. > thres. freq => ejected and KE equal to diff. between hf and hf(T)
current pattern in photoelectric effect freq above thres. => light greater intensity => greater current (current prop. to intensity of light

higher intensity => greater # photons per unit time => greater electrons eliminated
photoelectric effect on devices for visibility in low-level light detect low intensity ambient light (reflected by object being viewed) => amplify weak light => each photon => detector plate => eject electrons (electric field accelerates) => emits light => bright image
bohr model of H atom electron around circular orbit

centripetal force acting on electron as it revolves around nucleus = electrical force between + charged proton and - charged electron
Energy Level (H atom) orbital angular momentum of electron => energy of electron

electron changes only in discrete amounts w/ respect to quantum number

specific stable, or allowed, orbits of quantized (discrete) energy in which electrons did not radiate energy => energy level formula

energy levels of H given in eV
bohr energyin eV

corresponds to closet orbit to nucleus is -13.6 eV

energies farther away => less neg => greater => free from electrostatic (coulombic) => pull nucleus => positive energy (ionization)

0 energy => P and E separately completely => no attractive forcse

positive energy states => no principle quantum number => E not bound to P => free energy state => electron in quan. states => neg energy => attractive

energy of electron inc. farther from nucleus

n^2 inc => value inc.
quantized energy thought of change in GPE => change in height => discrete (quantized) changes of PE
orbit transferring an amount of energy exactly equal to difference in energy between on pathway to another
ground state smallest radius from nucleus
excited state higher energy orbit
orbital angular momentum of electron => L = nh/2pi
energy of electron E = -R(H)/n^(2)
energy levels of H in eV E(n) = -13.6 eV/ n^(2)
4 postulates of Bohr model1. Energy levels are stable and discrete, specific orbits

2. Electrons emits or absorbs when transition from one energy level to another

3. jump lower => higher; electron absorb a photon of precisely right freq. that photon energy (hf) equal energy diff. between two orbits

4. jump higher => lower; electron emits a photon of freq. such that photon's energy (hf) exactly energy difference between two orbits
change in electron's energy electron in lowest allowed energy level can't emit any more energy (although could absorb radiation and jump to higher)

E(f) - E(i)
Electron in excited state can either emit radiation when jumps down to lower energy

or

absorb radiation when it jumps to higher
emission of photon that has frequency bound-state energy levels are neg. if E is neg.

electron (neg) from higher, less neg. energy state (less tight bound state) to lower, more neg. energy state (more tightly bound state)

hf = -E
absorbed photon has freq. E is pos.

electron from lower, more neg to higher, less neg energy
fluorescence excite fluorescent substance w/ UV radiation => glow w/ visible light

UV radiation photons => high freq. (short wavelength) => after exciting higher energy state => electrons original in two or more steps (each less energy and lower freq (longer wavelength)) => if wavelength w/in visible range => light of particular color
energy of photons inc w/ increasing freq.
energy of photons converted into ejecting electron (amount required by work function will be given in problem), and any excess energy is converted into KE
negative frequency no such THING
Planck's constant h = 6.63 x 10^-34 J x s = 4.14 x 10^-15 eV x s

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