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Waves – Waves – transfer of eng without the net transfer of matter Mechanical waves – R equires a medium to propagate through Wave Amplitude – Amplitude – maximum displacement a particle in a mechanical wave has from its origin Periodic Wave – Source of disturbance undergoes continual oscillation producing a constant wave Light Properties – Eng, no mass, no charge
suggests light sources do not emit continuous waves of light b instead, discrete bundled particles of eng called photons. 1lanc( suggested$ )ne photon can interact with one electron at an moment
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1hotons deliver all their eng to electron upon interaction Total eng of light beam - number of photons (n) 2 hf
Wor+ function (W) – minimum eng %8& required for an electron to escape from an atom % W h f o& 'hreshold re9 (f o) – "inimum freq at which photoelectric effect starts to occur % specific to different atoms & When a light of fre9 f is shone on an atom: h f W ; E +
#
Therefore$
inear Aropagation %eection – The bending of a wave around a barrier, Diffraction – Diffraction
1
•
m(vma2)- h f – W
2
Einsteiner of photons, rather than the amplitude?energ= amplitude?energ= of a wave f hf @ W, left over eng0 given off as inetic eng (E +)
obstacle or through a single slit Path difference (PD) – (PD) – Difference in length from a point in an interference pattern to the source n phase – phase – sources produce produce waves at at the same freq where a crest meets a crest and a trough meets and trough !onstructive nterference – nterference – addition of of amplitudes arriving arriving in phase. Coherent has constant phase difference, Destructive nterference – nterference – Crest meets a trough, trough, amplitudes amplitudes cancel Antinode – Antinode – constructive constructive interference location "ode – "ode – Destructive interference interference location location
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809 E7 / h( : W E8#9 W = E2ntercept 819 ( : independent varia*le 849 h / gra+ient
•
•
•
Circumference of electron or*it =
Compton’s relationship: relationship:
w=
Increasing D = decreasing intensity, increasing fringe spacing ∝
λ S
# Increasing wavelength of
light used increases diffraction and hence w (fringe spacing)
λ S
≥
•
Only applies to objects with no mass , p = momentum of photon De Broglie replaced p with mv and postulated that matter had wavelengths as well
s
Diffraction
P=¿
h hf Energy Energy = = λ c c
2 D
Derived relationships:
$ means significant diffraction
Since! E" = P%&'&ELE!'! EE!' Photocurrent – current induced b action of light Photoelectron – electron emitted from substance illuminated b !"R
1 2
¿
h mv
=
h
√ 2 m E k
mv#
De Broglie found that the diraction pattern of x-rays was similar to those of electrons !ence the wavelengths of electrons "particles# was similar to -ve terminal towards cathode: Accelerating those of $-%ays "waves# &pectroscopes: 'mission()*sorption 'mission()*sorption voltage "voltage not &pectra++++++++++++++++ impeding as atoms a*sor* eng to promote their electrons to a photocurrent# higher eng state )s they fall *ac to ground level &wap terminals of *attery "ve terminal faces they release eng corresponding corresponding to dierent cathode# for -ve voltage at cathode "location of light# wavelengths of light . ;his gives the ma, E7 'lectrons can emit their eng in various com*inations Monochromatic light *se+ (or this e,periment #ve terminal towards cathode$ Accelerating voltage %voltage Because a*sorption not impeding photocurrent& photocurrent& is a singular process *topping voltage – 'ow much wor( done b load to stop and emission occurs photoelectrons photoelectrons from being emitted in multiple steps )*+ affected affected b freq of incident light %greater freq. - higher there are more stopping voltage possible emission lines than 1 $onisation level .eng level where an electron has E+ mv- * topping voltage (.) su/cient eng to overcome the electrostatic force 2 *inding it to the atom Stopping voltage %max speed& of fastest electrons ∝ Spectroscope . 0ualitatively measures light emitted (v-) Varying Intensity of incident light *y electrons "ore intensit %/m #& - greater photocurrent photocurrent because more RO%&B$V' R greater wave than V V higher (re) photons means more electrons can be e0ected ever second than R Emission spectra . *right *ands on a *acdrop ΔJ Δnh f of *lac corresponding to the eng released *y Power output of light: = P= t t electrons falling *ac to gro*n+ level "electron 1lanc(2s C onstant – h - 3.34 x 56 #47 8s9- 7.57 x 56 #5: e;< con1guration which gives the atom the most sta*ility and least eng# $e/ ($01 2 $3 #$4. ) – !ng gained b electron after it is moved Absorption spectra . dar *ands in the visi*le b 5; pd spectrum due to the a*sorption of speci1c 5$6 e/ to . ( !y "#$ % "& '") 5-6 . to e/ ( ÷ !y "#$ % wavelength of light *y an atom )toms emit the same amount of eng they a*sor* "& '") •
•
¿2π r
n- .stan+ing wave # forming a sta*le or*it
MATTER WAVES
Fringe spacing (w), Distance from screen (D), slit width (s)
)toms emit speci1c amounts of eng to promote their electrons to excited states 2f an atom does not a*sor* enough eng to promote its electrons to the next excitation state, it retains the eng as inetic eng for its electrons Electrons are unlikely are unlikely to to absorb eng in an e,cite+ state hence eng re)*ire+ to promote an electron to a certain e,cite+ state is always relative to the gro*n+ level 3or example: 4st excitation state = 5e6, 5 nd excitation state = 7ev Dierence in eng levels = 8e6 If an atoms 3ev, electrons will only be promoted to the 1st excitation state and retain 1ev as E k 2t will 9; *e promoted from the 4 st excitation state to the 5 nd *ecause it is unliely excited atoms a*sor* eng< even if the eng a*sor*ed is su/cient Dierence in successive eng levels *ecomes smaller as you move to higher eng level "n= and n=4 has the greatest dierence# dierence# &upport for the dual nature of matter++++++++++++++++++++ Discrete eng levels for particles "electrons# . 'lectrons moved in waves inside their eng levels "0uantised# &tanding waves are the eng levels electrons exist within< only certain > of light will promote electrons "resonance#
λ=
h mv
∴ n∙
h =2 π r mv
.n/0#1 '''2 n = 1 (grond level!, n=" (1 st excitation state!, etc# 2f an integral num*er of wavelengths cannot 1t into the circumference of electron or*it, destructive interference occurs and the or*it "wavelength# is not an eng level 3e(t to right! n /1456