 # Physics and the Quantum Mechanical Model Section 13.3

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Physics and the Quantum Mechanical Model Section 13.3
KEY TERMS: Amplitude Wavelength Frequency Electromagnetic Spectrum Emission Spectrum Photoelectric Effect Ground State

Key Concepts The product of frequency (ν) and wavelength (λ) always equals the speed of light (c) c = λ ν Line emission spectra illustrate the amount of quantized energy levels De Broglie proposed that all matter in motion has wavelength properties Photoelectric Effect – metals eject electrons called photoelectrons when light shines on them Only certain frequencies of light will demonstrate the photoelectric effect

Light and Atomic Spectra

Electromagnetic Spectrum and how wavelength relates to various objects

Speed of light = wavelength x frequency c = λ ν
Frequency = number of complete waves per unit of time Units = Hertz (Hz) or per second (sec-1) Amplitude = wave’s height from the origin Wavelength = The length of one complete wave cycle Units = Ǻ, nm, cm, m Wavelength (λ) and Frequency (ν) are inversely related Speed of light = wavelength x frequency c = λ ν As wavelength increases, frequency decreases

Electromagnetic Spectrum – various colors you see due to the wavelength of light
Emission Spectrum – line of color that correlates to one exact frequency

Photoelectric effect Max Planck studied this concept
Trying to describe why iron (or metals in general) changed color when heated Energy of a quantum = Planck’s constant x frequency E = h ν The size of the quantum being absorbed or emitted depends on the size of the energy change Small energy change = low frequency radiation Large energy change = high frequency radiation

Photoelectric Effect Albert Einstein
Proposed that light can be described as quanta of energy that behave as if they were particles Photons = light energy Metals eject electrons when specific wavelengths of light shines on them Electrons being ejected Light energy metal

Application of photoelectric effect:
Application of photoelectric effect: Photoelectric cells uses the energy of light to generate electricity for homes, vehicles, etc

Atomic Spectra Electrons absorb energy and get “excited”
When they are excited, they jump up to a new energy level (farther away from nucleus) The electron then loses that energy and falls back down to ground state The energy emitted produces the various colors of light that you see

Quantum Mechanics If light behaves as waves and particles, can particles behave as waves? Question proposed by De Broglie (French graduate student) All matter exhibits wavelike motions Particles gain or lose energy in packages called quanta Heisenberg uncertainty principle It is impossible to know exactly both the velocity and position of a particle at the same time