Review of Special Relativity S and S’ system: S and S’ system: For a particle with velocity in...
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Transcript of Review of Special Relativity S and S’ system: S and S’ system: For a particle with velocity in...
Review of Special Review of Special RelativityRelativity
SS and and S’S’ system: system:
For a particle with velocity in S:For a particle with velocity in S:
The Doppler effect:The Doppler effect:
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S’ moves with velocity v in S along the x-axis.
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When When θ =0, the course is =0, the course is moving away from the moving away from the observer.observer.
v
Electromagnetic radiation Electromagnetic radiation behaves as particlesbehaves as particles
1.1. Discussion about homework: problem 33, Discussion about homework: problem 33, page 64.page 64.
2.2. Quiz 9.09 and a few comments on quiz Quiz 9.09 and a few comments on quiz 9.04.9.04.
3.3. Topics in EM waves as particles:Topics in EM waves as particles: Blackbody radiation and Planck’s constant, Blackbody radiation and Planck’s constant,
Planck’s Nobel Prize in physics.Planck’s Nobel Prize in physics. The Photoelectric Effect and Einstein's Nobel The Photoelectric Effect and Einstein's Nobel
Prize in physics.Prize in physics. The X-rays and Roentgen’s Nobel Prize in The X-rays and Roentgen’s Nobel Prize in
physics.physics. The Compton Effect and Compton’s Nobel Prize The Compton Effect and Compton’s Nobel Prize
in physics.in physics. Pair production, energy to mass conversion and Pair production, energy to mass conversion and
Anderson’s Nobel Prize in physics.Anderson’s Nobel Prize in physics. The wave-particle duality and the door to yet The wave-particle duality and the door to yet
another new world.another new world.4.4. The first of the many topics for our class The first of the many topics for our class
projects.projects.
today
Blackbody radiation Blackbody radiation and Planck’s constantand Planck’s constant
Blackbody radiation:Blackbody radiation:Blackbody: that radiates but not reflects.Blackbody: that radiates but not reflects.Blackbody is a good approximation of Blackbody is a good approximation of many objects that radiate, hence its many objects that radiate, hence its surface temperature measured.surface temperature measured.
Spectral energy density of a blackbody radiation:Spectral energy density of a blackbody radiation: Measurements:Measurements: Classical theory:Classical theory:
UV diverging problem.UV diverging problem. Planck’s proposal: Planck’s proposal:
The energy at a certain frequency isThe energy at a certain frequency isWhere Where nn is an integer (quantum) and is an integer (quantum) and hh is the Planck’s constant. is the Planck’s constant.
The Planck’s constant The Planck’s constant
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The lava’s surface temperature can be measured by the radiation it emits.
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dU hf Vf
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346 63 10 J sh .
The Photoelectric EffectThe Photoelectric Effect
The photoelectric effect:The photoelectric effect:There is a frequency threshold onThere is a frequency threshold onthe light to produce this effect.the light to produce this effect.the electron density proportional tothe electron density proportional toThe light density. The light density.
Einstein’s explanationEinstein’s explanationEinstein’s proposal: each photonEinstein’s proposal: each photonbehaves like a particle with energybehaves like a particle with energy
The electron’s maximum kinetic energy isThe electron’s maximum kinetic energy is
is the work function of the material with which an electron is the work function of the material with which an electron can be freed from its surface. See table 3.1.can be freed from its surface. See table 3.1.
Example 3.1, work on the blackboard in class.Example 3.1, work on the blackboard in class.
Example 3.2, work on the blackboard in class.Example 3.2, work on the blackboard in class.
E hf
maxKE hf
The X-raysThe X-rays The X-rays: electromagnetic radiation from The X-rays: electromagnetic radiation from 33××10101616 to to 33××10101919 Hz. Hz. X-rays can be generated in many ways. One of them:X-rays can be generated in many ways. One of them:
High electrical potential is needed to accelerate electrons to High electrical potential is needed to accelerate electrons to hit the target.hit the target.
Photons produced by accelerating charges are called Photons produced by accelerating charges are called breamsstrahlungs. There is a cutoff wavelength associated breamsstrahlungs. There is a cutoff wavelength associated with the target material, indicating the quanta of the X-rays. with the target material, indicating the quanta of the X-rays.
Discussion and questionDiscussion and question
Photon energy is quantized to bePhoton energy is quantized to be
nn is an integer. is an integer. hh is Planck’s constant. is Planck’s constant. For a single photon: For a single photon:
Here energy is related to the Here energy is related to the electromagnetic wave’s frequency electromagnetic wave’s frequency ff, not , not its amplitude.its amplitude.
What is related to the wave amplitude? What is related to the wave amplitude? The light intensity.The light intensity.
E nhf
E hf
Review questionsReview questions In the text the spectral energy density of a In the text the spectral energy density of a
blackbody radiation is expressed as a function blackbody radiation is expressed as a function of the frequency: of the frequency:
WithWith , Can you change this formula to a , Can you change this formula to a function of wavelength? function of wavelength?
Einstein is famous for his theories of Special Einstein is famous for his theories of Special Relativity (1905) and General Relativity Relativity (1905) and General Relativity (1916), but he was award the Nobel Prize in (1916), but he was award the Nobel Prize in physics in 1921 for his work on photoelectric physics in 1921 for his work on photoelectric effect (1905). Do you know why? effect (1905). Do you know why?
23
8
1Bhf k T
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cf
Preview for the next Preview for the next classclass
Text to be read:Text to be read: In chapter 3:In chapter 3:
Section 3.4Section 3.4 Section 3.5Section 3.5 Section 3.6Section 3.6
Questions:Questions: Why the text claims that the Compton effect Why the text claims that the Compton effect
cannot be explained by classical EM theory?cannot be explained by classical EM theory? Who discovered positron? And What is a Who discovered positron? And What is a
positron? When an electron and a position positron? When an electron and a position meet, what happens? And what is a Positron meet, what happens? And what is a Positron Emission Tomography (PET)?Emission Tomography (PET)?
What is your opinion on this: a photon is an What is your opinion on this: a photon is an electromagnetic wave or a particle? electromagnetic wave or a particle?
Class project topic, 1Class project topic, 1
From X-ray to PET, Nobel Prize From X-ray to PET, Nobel Prize winning discovers in physics that winning discovers in physics that change people’s lives.change people’s lives.
Homework 4, due by 9/23Homework 4, due by 9/23
1.1. Problem 12 on page 93.Problem 12 on page 93.
2.2. Problem 17 on page 93.Problem 17 on page 93.
3.3. Problem 21 on page 93.Problem 21 on page 93.
4.4. Problem 29 on page 94. (an Problem 29 on page 94. (an example for this problem can be example for this problem can be found on page 79, may not be found on page 79, may not be discussed in the classroom)discussed in the classroom)