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Electromagnetic Spectrum Light as a Particle

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Learning Objectives Understand the electromagnetic spectrum Understand the relationships between wavelength, frequency, and energy of electromagnetic radiation Perform calculations involving wavelength, frequency, and energy of electromagnetic radiation Electromagnetic Spectrum

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Wave model explains much of the behavior of light – Does not explain why particular frequencies of light are absorbed or emitted in certain situations – Ex) Heating elements emit red light when a certain temperature is reached Light as a Particle

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In 1900, Max Planck investigated light emitted by heated objects – Theorized that energy is absorbed and released by particles in small discrete amounts called quanta Quanta – small discrete amounts of energy that can be absorbed or emitted by an atom Light as a Particle

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Planck derived an equation to relate energy of a quantum to frequency – The constant is Planck’s constant (h) Planck’s constant is in units of joules seconds, J s Frequency is in units of hertz, Hz, or inverse seconds Energy is in units of joules, J Energy is directly proportional to frequency Light as a Particle

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Relationship between energy and frequency explains why higher frequency electromagnetic radiation tends to be more damaging to cells Higher frequency radiation carries more energy – Ex) Gamma radiation is extremely damaging to cells – Ex) Radio waves are virtually harmless Light as a Particle

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In 1905, Albert Einstein concluded that electromagnetic radiation behaves as both a wave and a particle – Photon – mass-less particle of electromagnetic radiation that carries a quantum of energy – Energy of a photon can be determined by its frequency Light as a Particle

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Finding Energy, Given Frequency Ex) What is the energy of a photon of light with a frequency of 6.26 × 10 14 Hz? IV.Conversions needed? V.Intermediates needed? VI.Solve VII.Does the result make sense? I.Strategy II.Given and unknown III.Formula No. Yes.

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The Planck-Einstein equation can be used to determine energy of photons emitted or absorbed – Ex) Can find energies of photons emitted by atoms when excited atoms return to a lower energy state called the ground state Light as a Particle

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When passed through a prism, emitted photons are separated by frequency The frequencies of the photons can be measured and their energies calculated Light as a Particle

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Atomic emission spectrum: the pattern of frequencies obtained by passing light emitted by atoms of an element in the gaseous state through a prism Atomic emission spectra can be used to identify elements in unknown substances because each element has a unique atomic emission spectrum Light as a Particle

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Energy is directly proportional to frequency Wavelength and frequency are inversely proportional Wavelength is inversely proportional to energy Light as a Particle

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Combining the speed-of-light equation with the Planck- Einstein equation yields a formula showing the inverse relationship between wavelength and energy Equation Relating Energy to Wavelength

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Finding Energy from Wavelength Ex) What is the energy of a photon whose wavelength is 4.21 x 10 –7 m? IV.Conversions needed? V.Intermediates needed? VI.Solve VII.Does the result make sense? I.Strategy II.Given and unknown III.Formula No. Yes.

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Learning Objectives Understand the electromagnetic spectrum Understand the relationships between wavelength, frequency, and energy of electromagnetic radiation Perform calculations involving wavelength, frequency, and energy of electromagnetic radiation Electromagnetic Spectrum

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