Lecture 2010/19/05. wavelength Amplitude Node Electromagnetic Radiation (Light as waves) Moving...
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Transcript of Lecture 2010/19/05. wavelength Amplitude Node Electromagnetic Radiation (Light as waves) Moving...
c = λν
c = speed of light (3 x 108 m/s in a vacuum)
λ = wavelength (m)
ν = frequency (s-1 or Hertz, Hz)
Electromagnetic RadiationElectromagnetic Radiation
Red light has Red light has = 700 nm. Calculate the = 700 nm. Calculate the frequency.frequency.
Freq = 3.00 x 108 m/s
7.00 x 10-7 m 4.29 x 1014 sec-1Freq =
3.00 x 108 m/s
7.00 x 10-7 m 4.29 x 1014 sec-1
700 nm • 1 x 10 -9 m
1 nm = 7.00 x 10 -7 m700 nm •
1 x 10 -9 m
1 nm = 7.00 x 10 -7 m
Standing (stationary)
Waves
•Has 2 or more nodes
•Distance between nodes is λ/2.
•Distance between ends has to be n(λ/2)
a) Draw a standing wave with 1 node. What is the wavelength of this wave?
b) Draw a standing wave with 3 nodes between the ends. What is the wavelength?
c) If the wavelength of the standing wave is 2.5 cm, how many waves fit within the boundaries? How many nodes?
Visible Light
1. Which color in the visible spectrum has the highest frequency?
2. Is the wavelength of x-rays longer or shorter than UV?
The frequency of radiation used in microwave ovens is 2.45 GHz (1 gigahertz is 109 s-1.
What is the wavelength in nm of this radiation?
Light as particles
•Max Planck-
•Vibrations are quantized
•Planck’s constant
•E=hν = hc/λ
•E = energy (J)
•h = Planck’s constant
•6.626 x 10-34 J-s
Photoelectric EffectPhotoelectric Effect
Classical theory said that Energy of ejected electron should increase with increase in light intensity
NOT OBSERVED
No e- observed until light of a certain minimum E is usedNumber of e- ejected depends on light intensity.
Light consists of particles called PHOTONS of discrete energy.
Compare the energy of a mole of red light photons (λ= 700 nm) and a mole of UV photons (λ= 300 nm)
KJ/mol 1.399J/mole 399126E
e)photon/mol 1002.6(photon/J1062.6E
nm10
m 1)nm 300(
)sm1000.3)(sJ1063.6(E
2319
9
834
λ
hchνE
KJ/mol 171J/mole054171E
e)photon/mol 1002.6(photon/J1084.2E
nm10
m 1)nm 700(
)sm1000.3)(sJ1063.6(E
2319
9
834
λ
hchνE
Dual Nature of Light
Both wave and particle characteristics
WaveRefractionDiffraction
ParticlePhotoelectric effect
Balmer series
17
22
m100974.1)ttancons Rydberg( R
2n whereinteger, an is n
n
1
2
1R
λ
1
Rydberg equation
Balmer Series
Atomic Spectra and Atomic Spectra and BohrBohr
Atomic Spectra and Atomic Spectra and BohrBohr
1.1. Any orbit should be possible and so is any energy.Any orbit should be possible and so is any energy.
2.2. But a charged particle moving in an electric field But a charged particle moving in an electric field should emit energy. should emit energy.
Electron would eventually run out of energyElectron would eventually run out of energy
+Electronorbit
BohrBohr
New theory : New theory : Quantum or Wave Mechanicse- can only exist in certain discrete orbits e- can only exist in certain discrete orbits
Stationary statesStationary states e- is restricted to e- is restricted to QUANTIZEDQUANTIZED energy states. energy states.
levelenergy n
light of speed c
constant sPlanck'h
m100974.1constant RydbergR
n
RhcE
n
1
n
1hcR
n
1
n
1Rhc
λ
1hc
λ
hcE
n
1
n
1R
λ
1
7
2n
22
21
22
21
22
21
n= principal quantum numbern is an integern with the lowest possible energy is said to
be in the ground state
Electrons with higher energy than ground state are said to be in an excited state
Calculate the energies of n=1, n=2, and n=3 states of the hydrogen atom in J/atom.
R = 1.097 x 107 m-1
h = 6.626 x 10-34 J-s
c = 2.998 x 108 m/s
s/m10998.2light of speed c
sJ1062.6constant sPlanck'h
m100974.1constant RydbergR
2n and 1n
n
1
n
1Rhc
n
Rhc
n
RhcEEE
8
34
7
2initial
2final
2initial
2final
initialfinal
Moving between energy levels