Electromagnetic Spectrum Light as a Particle

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

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

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

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

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

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

Finding Energy, Given Frequency Ex) What is the energy of a photon of light with a frequency of 6.26 × 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.

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

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

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

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

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

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.

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