Photo-Electric Facts
Photo-Electric/Planck’s Constant Lab No electrons are emitted if the incident light frequency is below some cutoff frequency that is characteristic of the material being illuminated
The maximum kinetic energy of the photoelectrons is independent of the light intensity
The maximum kinetic energy of the photoelectrons increases with increasing light frequency
Electrons are emitted from the surface almost instantaneously, even at low intensities Einstein’s Explanation A tiny packet of light energy, called a photon, would be emitted when a quantized oscillator jumped from one energy level to the next lower one The photon’s energy would be E = hƒ Each photon can give all its energy to one electron in the metal
Max Planck Arthur Holly Compton
1858 – 1947 1892 – 1962
Introduced a Discovered the “quantum of Compton effect action,” h Worked with cosmic rays Awarded Nobel Prize in 1918 for Director of the lab at U of Chicago discovering the quantized nature Shared Nobel Prize in 1927 of energy
Compton Scattering Louis de Broglie
Compton assumed 1892 – 1987 the photons acted like other particles Discovered the in collisions wave nature of Energy and electrons momentum were Awarded Nobel conserved Prize in 1929 The shift in wavelength is
h o (1 cos ) mce
1 Quick Quiz de Broglie Wavelength and What is the value of Planck’s Constant? Frequency -19 A. 1.6 x 10 Coulombs The de Broglie wavelength of a -34 B. 6.6 x 10 Joule-sec particle is hh C. 340 m/sec 8 D. 3 x 10 m/s pmv The frequency of matter waves is E ƒ h
The Davisson-Germer Experiment
They scattered low-energy electrons from a nickel target The Electron Microscope They followed this with extensive diffraction measurements from various materials The electron microscope depends on the wave The wavelength of the electrons calculated from characteristics of electrons the diffraction data agreed with the expected de Microscopes can only Broglie wavelength resolve details that are This confirmed the wave nature of electrons slightly smaller than the wavelength of the radiation Other experimenters have confirmed the wave nature of other particles used to illuminate the object The electrons can be accelerated to high energies and have small wavelengths
Erwin Schrödinger Werner Heisenberg
1901 – 1976 1887 – 1961 Developed an abstract Best known as the creator mathematical model to of wave mechanics explain wavelengths of Worked on problems in spectral lines
general relativity, Called matrix cosmology, and the mechanics application of quantum Other contributions mechanics to biology Uncertainty Principle “Wave Function” is what is! Nobel Prize in 1932
Atomic and nuclear models
Forms of molecular hydrogen
2 The Uncertainty Principle Thought Experiment The Uncertainty Principle Mathematically, h xp x 4 It is physically impossible to measure simultaneously the exact position and the exact linear momentum of a particle Another form of the principle deals with energy and time: h A thought experiment for viewing an electron with a Et powerful microscope 4 In order to see the electron, at least one photon must bounce off it During this interaction, momentum is transferred from the photon to the electron Therefore, the light that allows you to accurately locate the electron changes the momentum of the electron
Uncertainty Principle Today’s Lab Applied to an Electron
View the electron as a particle
Its position and velocity cannot both be know precisely at the same time
Its energy can be uncertain for a period given by t = h / (4 E)
Using a Tuning Fork to Producing a Sound Wave Produce a Sound Wave
Sound waves are longitudinal waves A tuning fork will produce a traveling through a medium pure musical note As the tines vibrate, they A tuning fork can be used as an disturb the air near them example of producing a sound wave As the tine swings to the right, it forces the air molecules near it closer together
This produces a high density area in the air
This is an area of compression
3 Using a Tuning Fork, cont. Using a Tuning Fork, final
As the tine moves toward the left, the air molecules to the right of the tine spread out As the tuning fork continues to vibrate, a This produces an area succession of compressions and rarefactions of low density spread out from the fork This area is called a A sinusoidal curve can be used to represent rarefaction the longitudinal wave Crests correspond to compressions and troughs to rarefactions
Standing Waves When a traveling wave reflects back on itself, it creates traveling waves in both directions
Speed of Sound in Air The wave and its reflection interfere according to the superposition principle
mT With exactly the right frequency, the wave will appear v 331 to stand still sK273 This is called a standing wave 331 m/s is the speed of sound at A node occurs where the two traveling waves have the 0° C same magnitude of displacement, but the displacements are in opposite directions T is the absolute temperature Net displacement is zero at that point
The distance between two nodes is ½λ
An antinode occurs where the standing wave vibrates at maximum amplitude
Other Examples of Forced Vibrations Resonance
A system with a driving force will Child being pushed on a swing
force a vibration at its frequency Shattering glasses
When the frequency of the driving Tacoma Narrows Bridge collapse force equals the natural frequency due to oscillations by the wind of the system, the system is said Upper deck of the Nimitz Freeway to be in resonance collapse due to the Loma Prieta earthquake
4 Standing Waves in Air Columns Tube Closed at One End
If one end of the air column is closed, a node must exist at this end since the movement of the air is restricted
If the end is open, the elements of the air have complete freedom of movement and an antinode exists
Resonance in an Air Column Closed at One End Quick Quiz In the lab today, what is in resonance? The closed end must be a node A. Water and air The open end is an antinode B. Sound waves going in 1 direction v fn nƒ n 1, 3, 5, C. Tuning fork and air in room n 4L 1 D. Tuning fork and air in column There are no even multiples of the fundamental harmonic
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