Review of Special Relativity S and S’ system: S and S’ system: For a particle with velocity in S: For a particle with velocity in S: The Doppler effect: The Doppler effect: S’ moves with velocity v in S along the x-axis. When =0, the course is moving away from the observer. When θ =0, the course is moving away from the observer.

Electromagnetic radiation behaves as particles 1. Discussion about homework: problem 33, page Quiz 9.09 and a few comments on quiz Topics in EM waves as particles:  Blackbody radiation and Planck’s constant, Planck’s Nobel Prize in physics.  The Photoelectric Effect and Einstein's Nobel Prize in physics.  The X-rays and Roentgen’s Nobel Prize in physics.  The Compton Effect and Compton’s Nobel Prize in physics.  Pair production, energy to mass conversion and Anderson’s Nobel Prize in physics.  The wave-particle duality and the door to yet another new world. 4. The first of the many topics for our class projects. today

Blackbody radiation and Planck’s constant Blackbody radiation: Blackbody radiation: Blackbody: that radiates but not reflects. Blackbody is a good approximation of many objects that radiate, hence its 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. Planck’s proposal: Planck’s proposal: The energy at a certain frequency is Where n is an integer (quantum) and h is the Planck’s constant. The Planck’s constant The Planck’s constant The lava’s surface temperature can be measured by the radiation it emits.

The Photoelectric Effect The photoelectric effect: The photoelectric effect: There is a frequency threshold on the light to produce this effect. the electron density proportional to The light density. Einstein’s explanation Einstein’s explanation Einstein’s proposal: each photon behaves like a particle with energy The electron’s maximum kinetic energy is is the work function of the material with which an electron can be freed from its surface. See table 3.1. is the work function of the material with which an electron 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.

The X-rays The X-rays: electromagnetic radiation from 3×10 16 to 3×10 19 Hz. The X-rays: electromagnetic radiation from 3×10 16 to 3×10 19 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 hit the target. Photons produced by accelerating charges are called breamsstrahlungs. There is a cutoff wavelength associated with the target material, indicating the quanta of the X-rays. Photons produced by accelerating charges are called breamsstrahlungs. There is a cutoff wavelength associated with the target material, indicating the quanta of the X-rays.

Discussion and question Photon energy is quantized to be Photon energy is quantized to be n is an integer. h is Planck’s constant. For a single photon: Here energy is related to the electromagnetic wave’s frequency f, not its amplitude. Here energy is related to the electromagnetic wave’s frequency f, not its amplitude. What is related to the wave amplitude? The light intensity. What is related to the wave amplitude? The light intensity.

Review questions In the text the spectral energy density of a blackbody radiation is expressed as a function of the frequency: In the text the spectral energy density of a blackbody radiation is expressed as a function of the frequency: With, Can you change this formula to a function of wavelength? Einstein is famous for his theories of Special Relativity (1905) and General Relativity (1916), but he was award the Nobel Prize in physics in 1921 for his work on photoelectric effect (1905). Do you know why? Einstein is famous for his theories of Special Relativity (1905) and General Relativity (1916), but he was award the Nobel Prize in physics in 1921 for his work on photoelectric effect (1905). Do you know why?

Preview for the next class Text to be read: Text to be read: In chapter 3: In chapter 3: Section 3.4 Section 3.4 Section 3.5 Section 3.5 Section 3.6 Section 3.6 Questions: Questions: Why the text claims that the Compton effect cannot be explained by classical EM theory? Why the text claims that the Compton effect cannot be explained by classical EM theory? Who discovered positron? And What is a positron? When an electron and a position meet, what happens? And what is a Positron Emission Tomography (PET)? Who discovered positron? And What is a positron? When an electron and a position meet, what happens? And what is a Positron Emission Tomography (PET)? What is your opinion on this: a photon is an electromagnetic wave or a particle? What is your opinion on this: a photon is an electromagnetic wave or a particle?

Class project topic, 1 From X-ray to PET, Nobel Prize winning discovers in physics that change people’s lives. From X-ray to PET, Nobel Prize winning discovers in physics that change people’s lives.

Homework 4, due by 9/23 1. Problem 12 on page Problem 17 on page Problem 21 on page Problem 29 on page 94. (an example for this problem can be found on page 79, may not be discussed in the classroom)