Light as a Particle. Objectives  Define a quantum  Calculate the energy of a photon  Relate photon energy to wavelength and frequency of EMR.

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Presentation transcript:

Light as a Particle

Objectives  Define a quantum  Calculate the energy of a photon  Relate photon energy to wavelength and frequency of EMR

Blackbody Radiation  It was known that as one heats an object it changes color. What colors can you name as objects heat up?  The color corresponds to the emission of EMR. As the object gets hotter it should emit greater and greater frequencies of EMR.

Classical Physics – light, energy, heat, forces, electricity and magnetism – Everything had been explained as far as scientists thought

 A problem that classical physics could not explain was: the mathematical relationship between the temperature of a material and the colour of light that material gives off

 According to classical physics, the radiation emitted from an incandescent object is caused by the oscillation of the atoms and molecules that make it up.

 The color corresponds to the emission of EMR. As the object gets hotter it should emit greater and greater frequencies of EMR.

 called Ultraviolet catastrophe

What actually happened  intensity increases until it reaches a peak intensity that depends on temperature, then it drops off sharply

blackbody  – a perfect absorber: an object that completely absorbs all wavelengths of EMR that strike it (all the energy) and when heated, that energy is re-emitted as EMR

Max Planck – (early 1900’s)  Planck assumed that the energy given off by these objects had to occur in discreet units (bundles) of energy.

EMR could only vibrate at certain discrete frequencies. Planck called the smallest amount of energy a quantum. One quantum of light is called a photon. Quanta

Planck’s Formula  the energy emitted by a vibrating atom can be explained by the following equation The energy of a single quantum of EMR at a specific frequency or wavelength

Vibrating at some frequency atom So an EM wave is analyzed by the following equations: To determine the energy of multiple pieces or quanta: E = nhf n = number of pieces of radiation emitted or number of quanta

Examples: Eg) Determine the energy emitted by a photon of green light having a wavelength of 518nm.

Eg) What is the wavelength of a 6.75 eV photon? ( Recall: 1 eV = 1.60 x J) Reading: Text: p Assignment: p. 710 #1 – 6