Ch_07b - Continuous Spectra White light passed through a...

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19 Continuous Spectra White light passed through a prism produces a spectrum – colors in co nt in uo us form. λ ~ 650 nm λ ~ 575 nm λ ~ 500 nm λ ~ 480 nm λ ~ 450 nm 20 Light from an electrical discharge through a gaseous element (e.g., neon light, hydrogen lamp) does not contain all wavelengths. The spectrum is discontinuous ; there are big gaps. Line Spectra
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21 The pattern of lines emitted by excited atoms of an element is unique = atomic emission spectrum Line Spectra 22 Black Body Radiation Planck proposed that the vibrating atoms in a heated solid could absorb or emit electromagnetic energy only in discrete amounts The smallest amount of energy, a quantum, is given by: E = hv where h is Planck’s constant: = 6.626 × 10 –34 J s Blackbody radiation depends on T of the emitting body. It is composed of all wavelengths. • Classical physics could not explain the intensity and frequency dependence.
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23 Photoelectric Effect Only photons with a frequency above a threshold limit will cause current flow 24 Quantum Theory – Photoelectric Effect Energy of photon is E = hv Einstein considered electromagnetic energy to be bundled into little packets called photons • The photoelectric effect arises when photons of light striking a surface transfer their energy to surface electrons. • … but an electron can escape only if the photon provides enough energy.
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25 What is the energy per photon and per mole of photons of violet light, with a wavelength of 415 nm? 26 • Light would be emitted as electrons circles the nucleus • Electron would eventually spiral into the nucleus Classical physics predicts the nuclear model is unstable
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27 Bohr’s Hydrogen Atom Niels Bohr found that the electron energy ( E n ) was quantized, that is, that it can have only certain specified values.
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Ch_07b - Continuous Spectra White light passed through a...

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