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Light: Physics and Quantum Mechanics Overview

Explore the properties of light, wavelength, frequency, atomic spectra, emission spectra, energy, and quantum mechanics in the context of the quantum mechanical model. Understand how light behaves as both waves and particles in this detailed guide.

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Light: Physics and Quantum Mechanics Overview

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  1. 5.3 Physics and the Quantum Mechanical Model

  2. Light • By 1900 enough experimental evidence to convince scientists that light consists of waves

  3. Wavelength (λ, Greek symbol Lambda) • Measured in m or nm • Frequency (ν, Greek symbol nu) • # waves per unit of time • Measured in cycles per second • SI unit = hertz (Hz) • Reciprocal second, s-1 • Amplitude = height from zero to crest

  4. C = νλ • Frequency and wavelength are inversely proportional to each other • All electromagnetic waves travel in a vacuum at a speed of c = 2.998 x 108 m/s

  5. Electromagnetic Spectrum • Wave model  light is made up of electromagnetic waves • Visible light ranges from red (low energy, 700 nm) to violet (high energy, 380 nm)

  6. Atomic Spectra • Atoms absorb energy, e- move to higher energy levels. • e- lose energy by giving off light as they return to lower energy levels • Light emitted by atoms is a mixture of specific frequencies, each frequency corresponds to a certain color • Emission spectrum

  7. Emission spectrum of an element is like a fingerprint, no two elements have the same • Used to identify elements

  8. Lowest possible energy of electron is its Ground State • Absorbs energy and moves to EXCITED STATE • Quantum of energy (light) emitted when electron drops back to lower energy level • Emission takes place in an abrupt step called electronic transition

  9. Energy and Frequency • Photon - A quantum of light (packet of energy) • The light emitted has a frequency directly proportional to energy change of electron > Frequency >Energy

  10. Energy per photon ∆E = hc/λ ∆E = hν h = 6.626 x 10-34 J ∙ s/photon (h = Planck’s constant)

  11. Lyman series- transition to n = 1 (ultraviolet) • Balmer series- transition to n = 2 (visible) • Paschen series- transition to n = 3 (infrared)

  12. Quantum Mechanics • De Broglie predicted that all moving objects have wavelike behavior • Classical mechanics describes the motions of bodies much larger than atoms • Quantum mechanics describes the motions of subatomic particles and atoms as waves

  13. Heisenberg uncertainty principle-it is impossible to know exactly both the velocity and the position of a particle at the same time

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