Phy106Light-Photons

Phy106Light-Photons - The Wave Particle Duality OR Light...

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Unformatted text preview: The Wave Particle Duality OR Light Waves Until about 1900, the classical wave theory of light described most observed phenomenon. Until about 1900, the classical wave theory of light described most observed phenomenon. Light waves: Characterized by: Amplitude (A) Frequency ( ) Wavelength ( ) Energy A 2 And then there was a problem However, in the early 20 th century, several effects were observed which could not be understood using the wave theory of light. Two of the more influential observations were: 1) The Photo-Electric Effect 2) The Compton Effect I will describe each of these today Vary wavelength, fixed amplitude electrons emitted ? What if we try this ? Photoelectric Effect (I) No electrons were emitted until the frequency of the light exceeded a critical frequency, at which point electrons were emitted from the surface! (Recall: small large ) No Yes, with low KE Yes, with high KE Increase energy by increasing amplitude Classical Method electrons emitted ? No No No No Photoelectric Effect (II) Electrons are attracted to the (positively charged) nucleus by the electrical force In metals, the outermost electrons are not tightly bound, and can be easily liberated from the shackles of its atom. It just takes sufficient energy Classically, we increase the energy of an EM wave by increasing the intensity (e.g. brightness) Energy A 2 But this doesnt work ?? But this doesnt work ?? PhotoElectric Effect (III) An alternate view is that light is acting like a particle The light particle must have sufficient energy to free the electron from the atom. Increasing the Amplitude is just simply increasing the number of light particles, but its NOT increasing the energy of each one! Increasing the Amplitude does diddly-squat! However, if the energy of these light particle is related to their frequency, this would explain why higher frequency light can knock the electrons out of their atoms, but low frequency light cannot An alternate view is that light is acting like a particle The light particle must have sufficient energy to free the electron from the atom. Increasing the Amplitude is just simply increasing the number of light particles , but its NOT increasing the energy of each one ! Increasing the Amplitude does diddly-squat! However, if the energy of these light particle is related to their frequency , this would explain why higher frequency light can knock the electrons out of their atoms, but low frequency light cannot Photo-Electric Effect (IV) Light particle Before Collision After Collision In this quantum-mechanical picture, the energy of the light particle (photon) must overcome the binding energy of the electron to the nucleus....
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Phy106Light-Photons - The Wave Particle Duality OR Light...

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