《Blackbody Radiation Photoelectric Effect Wave-Particle Duality黑体辐射的光电效应的波粒二象性.ppt》由会员分享，可在线阅读，更多相关《Blackbody Radiation Photoelectric Effect Wave-Particle Duality黑体辐射的光电效应的波粒二象性.ppt（29页珍藏版）》请在三一文库上搜索。
1、Blackbody Radiation Photoelectric Effect Wave-Particle Duality,sections 30-1 30-4,Physics 1161: Lecture 28,Everything comes unglued,The predictions of “classical physics” (Newtons laws and Maxwells equations) are sometimes WRONG. classical physics says that an atoms electrons should fall into the nu
2、cleus and STAY THERE. No chemistry, no biology can happen. classical physics says that toaster coils radiate an infinite amount of energy: radio waves, visible light, X-rays, gamma rays,The source of the problem,Its not possible, even “in theory” to know everything about a physical system. knowing t
3、he approximate position of a particle corrupts our ability to know its precise velocity (“Heisenberg uncertainty principle”) Particles exhibit wave-like properties. interference effects!,Quantum Mechanics!,At very small sizes the world is VERY different! Energy can come in discrete packets Everythin
4、g is probability; very little is absolutely certain. Particles can seem to be in two places at same time. Looking at something changes how it behaves.,Hot objects glow (toaster coils, light bulbs, the sun). As the temperature increases the color shifts from Red to Blue. The classical physics predict
5、ion was completely wrong! (It said that an infinite amount of energy should be radiated by an object at finite temperature.),Blackbody Radiation,Blackbody Radiation Spectrum,Visible Light: 0.4mm to 0.7mm,Higher temperature: peak intensity at shorter l,Blackbody Radiation: First evidence for Q.M.,Max
6、 Planck found he could explain these curves if he assumed that electromagnetic energy was radiated in discrete chunks, rather than continuously. The “quanta” of electromagnetic energy is called the photon. Energy carried by a single photon is E = hf = hc/ Plancks constant: h = 6.626 X 10-34 Joule se
7、c,Preflights 28.1, 28.3,A series of light bulbs are colored red, yellow, and blue. Which bulb emits photons with the most energy? The least energy?,Which is hotter? (1) stove burner glowing red (2) stove burner glowing orange,Preflights 28.1, 28.3,A series of light bulbs are colored red, yellow, and
8、 blue. Which bulb emits photons with the most energy? The least energy?,Which is hotter? (1) stove burner glowing red (2) stove burner glowing orange,Blue! Lowest wavelength is highest energy. E = hf = hc/l,Red! Highest wavelength is lowest energy.,Hotter stove emits higher-energy photons (shorter w
9、avelength = orange),Three light bulbs with identical filaments are manufactured with different colored glass envelopes: one is red, one is green, one is blue. When the bulbs are turned on, which bulbs filament is hottest?,Red Green Blue Same,Three light bulbs with identical filaments are manufacture
10、d with different colored glass envelopes: one is red, one is green, one is blue. When the bulbs are turned on, which bulbs filament is hottest?,Red Green Blue Same,Colored bulbs are identical on the inside the glass is tinted to absorb all of the light, except the color you see.,A red and green lase
11、r are each rated at 2.5mW. Which one produces more photons/second?,Red Green Same,A red and green laser are each rated at 2.5mW. Which one produces more photons/second?,Red Green Same,Red light has less energy/photon so if they both have the same total energy, red has to have more photons!,Wiens Dis
12、placement Law,To calculate the peak wavelength produced at any particular temperature, use Wiens Displacement Law:,T peak = 0.2898*10-2 mK,temperature in Kelvin!,For which work did Einstein receive the Nobel Prize?,Special Relativity E = mc2 General Relativity Gravity bends Light Photoelectric Effec
13、t Photons Einstein didnt receive a Nobel prize.,For which work did Einstein receive the Nobel Prize?,Special Relativity E = mc2 General Relativity Gravity bends Light Photoelectric Effect Photons Einstein didnt receive a Nobel prize.,Photoelectric Effect,Light shining on a metal can “knock” electron
14、s out of atoms. Light must provide energy to overcome Coulomb attraction of electron to nucleus Light Intensity gives power/area (i.e. Watts/m2) Recall: Power = Energy/time (i.e. Joules/sec.),Photoelectric Effect,Light Intensity,Kinetic energy of ejected electrons is independent of light intensity N
15、umber of electrons ejected does depend on light intensity,Threshold Frequency,Glass is not transparent to ultraviolet light Light in visible region is lower frequency than ultraviolet There is minimum frequency necessary to eject electrons,Difficulties With Wave Explanation,effect easy to observe wi
16、th violet or ultraviolet (high frequency) light but not with red (low frequency) light rate at which electrons ejected proportional to brightness of light The maximum energy of ejected electrons NOT affected by brightness of light electrons energy depends on lights frequency,Photoelectric Effect Sum
17、mary,Each metal has “Work Function” (W0) which is the minimum energy needed to free electron from atom. Light comes in packets called Photons E = h f h=6.626 X 10-34 Joule sec Maximum kinetic energy of released electrons hf = KE + W0,If hf for the light incident on a metal is equal to the work funct
18、ion, what will the kinetic energy of the ejected electron be?,the kinetic energy would be negative the kinetic energy would be zero the kinetic energy would be positive no electrons would be released from the metal,If hf for the light incident on a metal is less than the work function, what will the
19、 kinetic energy of the ejected electron be?,the kinetic energy would be negative the kinetic energy would be zero the kinetic energy would be positive no electrons would be released from the metal,If hf for the light incident on a metal is less than the work function, what will the kinetic energy of
20、 the ejected electron be?,the kinetic energy would be negative the kinetic energy would be zero the kinetic energy would be positive no electrons would be released from the metal,Photoelectric: summary table,Wave Particle Result Increase Intensity Rate Increase Increase Increase KE Increase Unchange
21、d Unchanged Increase Frequency Rate Unchanged Increase Increase KE Unchanged Increase Increase,Light is composed of particles: photons,Is Light a Wave or a Particle?,Wave Electric and Magnetic fields act like waves Superposition, Interference and Diffraction Particle Photons Collision with electrons
22、 in photo-electric effect Both Particle and Wave !,The approximate numbers of photons at each stage are (a) 3 103, (b) 1.2 104, (c) 9.3 104, (d) 7.6 105, (e) 3.6 106, and (f) 2.8 107.,Are Electrons Particles or Waves?,Particles, definitely particles. You can “see them”. You can “bounce” things off them. You can put them on an electroscope. How would know if electron was a wave?,Look for interference!,