1Light and Quantized Energy

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Electromagnetic Electromagnetic RadiationRadiation

Electromagnetic Electromagnetic RadiationRadiation

• Electromagnetic radiation: A form of Electromagnetic radiation: A form of energy that exhibits wavelike behavior as energy that exhibits wavelike behavior as it travels through spaceit travels through space

• Light: a form of electromagnetic radiationLight: a form of electromagnetic radiation

3What are some What are some examples of examples of

electromagnetic electromagnetic radiation?radiation?

What are some What are some examples of examples of

electromagnetic electromagnetic radiation?radiation?

What else?What else?

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• Waves have a frequencyWaves have a frequency

• Use the Greek letter Use the Greek letter ““nunu””, , , for frequency, , for frequency, and units are and units are ““cycles per seccycles per sec””

stand for wavelength – it’s the shortest distance between equivalent points on a continuous wave

• All radiation: All radiation: c = c = • • where c = velocity of light = 3.00 x 10where c = velocity of light = 3.00 x 1088 m/sec m/sec

Electromagnetic Electromagnetic RadiationRadiation

Electromagnetic Electromagnetic RadiationRadiation

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wavelength Visible light

wavelength

Ultaviolet radiation

Amplitude

Node

Electromagnetic Electromagnetic RadiationRadiation

Electromagnetic Electromagnetic RadiationRadiation

Crest

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ElectroElectromagneticmagnetic SpectrumSpectrum

ElectroElectromagneticmagnetic SpectrumSpectrum

In increasing energy, RIn increasing energy, ROOYY GG BBIIVV

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Electromagnetic Electromagnetic SpectrumSpectrum

Electromagnetic Electromagnetic SpectrumSpectrum

Long wavelength --> small frequencyLong wavelength --> small frequency

Short wavelength --> high frequencyShort wavelength --> high frequency

increasing increasing frequencyfrequency

increasing increasing wavelengthwavelength

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Practice Problems

1. What is the frequency of green light, which has a wavelength of 4.90 x 10-7m?

2. What is the speed of an electromagnetic wave that has a frequency of 7.8 x 106 Hz?

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Quantum ConceptQuantum ConceptQuantum ConceptQuantum Concept

• 1900 German physicist Max 1900 German physicist Max Planck started to search for Planck started to search for WHY light emitted from WHY light emitted from heated objects.heated objects.

• Found that Found that QUANTUM QUANTUM is the is the minimum amount of energy minimum amount of energy that can be gained or lost by that can be gained or lost by an atoman atom

• Matter can gain or lose energy Matter can gain or lose energy in small specific amounts in small specific amounts called quantacalled quanta

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Quantum ConceptQuantum ConceptQuantum ConceptQuantum Concept

• Planck showed mathematically that the energy Planck showed mathematically that the energy of a quantum is related to the frequency of the of a quantum is related to the frequency of the emitted radiation.emitted radiation.

EEquantumquantum = h = hE = energyE = energyh = Planckh = Planck’’s constant = 6.626 x 10s constant = 6.626 x 10-34-34 J·s J·s

= frequency= frequency

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Photoelectric ConceptPhotoelectric ConceptPhotoelectric ConceptPhotoelectric Concept

• Photoelectric effect: photons are Photoelectric effect: photons are emitted from a metalemitted from a metal’’s surface when s surface when light of a certain frequency shines on a light of a certain frequency shines on a surfacesurface

• Albert Einstein proposed that Albert Einstein proposed that electromagnetic radiation has both electromagnetic radiation has both wavelike and particlelike natures. He wavelike and particlelike natures. He calculated that the photon energy was:calculated that the photon energy was:

EEphoton =photon = h h

12Electromagnetic radiation.

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• ““Ground State” – lowest energy stateGround State” – lowest energy state• ““Excited State” – Electrons jump to Excited State” – Electrons jump to

higher energy levels due to an input of higher energy levels due to an input of energyenergy

• Absorption – amount of E absorbed to Absorption – amount of E absorbed to “boost” e- to higher E level (excited “boost” e- to higher E level (excited state)state)

• Emission – e- releasing E when “falling” Emission – e- releasing E when “falling” back to lower E level (ground state)back to lower E level (ground state)

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Bohr model

• Studying H atom emission spectrum Studying H atom emission spectrum lead to Bohr’s model – lead to Bohr’s model – • electrons are restricted to certain electrons are restricted to certain

orbits corresponding to E levelsorbits corresponding to E levels

Rutherford never explained Rutherford never explained how e- fill space surroundinghow e- fill space surroundingthe nucleusthe nucleus

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Practice Problems

1. What is the energy for each of the following types of radiation?a. 6.32 x 1020 s-1 b. 9.50 x 1013 Hz c. 1.05 x 1016 s-1