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Quantum Physics

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Quantum Physics

  1. 1. Team Members: 1.Abubakar Siddique Monir ID:163-15-8318 2.Md.Jahid Hasan Miah ID:163-15-8529 3.Sahariar Islam ID:163-15-8426 4.Mst.Sirazam Manira ID:163-15-8466 5.Muslima Tuz Zahra 163-15-7724
  2. 2. MILESTONES OF QUANTUM PHYSICS : J.J.Thomson Established electron as a fundamental particle of nature. He measured its charge to mass ratio using a Crooke's tube. Electric current = flow of electrons Animation of electrons moving and being deflected by an electric or magnetic field. Crooke's tube: Evacuated tube Visualization of electron beam
  3. 3. The other great theory of modern physics Deals with very small objects  Electrons, atoms, molecules Grew out of problems that seemed simple  Black-body radiation  Photoelectric Effect  Atomic Spectra Produces some very strange results…
  4. 4. OUR QUANTUM WORLD In the 20th century, study of atomic systems required a fundamental revision of these classical ideas about physical objects. 1. Light waves exhibited particle like properties – phenomena called photo-electric effect in which light impinging on certain metals cause instanteous emission of electrons in a billiard ball like impact. – the basis of automatic door openers in grocery stores 2. Electrons (particles) exhibit wave like properties – they can pass through each other ! Phenomenon of electron interference – basis of electron microscopes
  5. 5. The Quantum of Light or the Photon : Particle nature of light was proposed by Einstein in 1905 to explain the photo-electric effect. Photo-electric effect – automatic door openers in grocery stores. Particles of light are called light quanta or photons Energy of a Photon = h (frequency of light) h is a fundamental constant of nature and it is very small in size.
  6. 6. THE BOHR ATOM: Bohr proposed a revolutionary model: An atom with discrete (Quantum) states – an ad hoc model Bohr’s atom model achieved three important results: 1. Atoms are stable 2. Different atoms of the same element are identical. 3. Atoms regenerate if they are taken apart and then allowed to reform.
  7. 7. Photoelectric Effect When light shines on a metal surface, the surface emits electrons. For example, I can measure a current in a circuit just by shining a light on a metal plate.
  8. 8. Einstein successful explained the photoelectric effect within the context of quantum physics. Einstein proposed that light delivers its energy in chunks; light consists of little particles, or quanta, called photons, each with an energy of Planck's constant times its frequency. E = h f h: Planck’s constant F: Frequency of Radiation E: Energy h = 6.6 x 10-34 J.s.
  9. 9. Quantum Physics: the “quantum” comes from quantization: we need to understand the origin of this. The Photoelectric Effect metal light Electron detector electrons
  10. 10. metal light Electron detector electrons Actual Experimental Observations: [1] There is no delay between the light hitting the surface and the electrons being ejected [2] Electrons are ejected only if the incident light has a frequency above some threshold value (i.e., it depend on the color of the light!!)
  11. 11. Observations: 1) Number of electrons depends on intensity 2) Energy of electrons DOES NOT depend on intensity3) Cut-off frequency: minimum frequency to get any emission 4) Above cut-off, energy increases linearly with frequency
  12. 12. Observations: 1) Number of electrons depends on intensity 2) Energy of electrons DOES NOT depend on intensity 3) Cut-off frequency: minimum frequency to get any emission 4) Above cut-off, energy increases linearly with frequency Higher intensity More quanta Only one photon to eject 𝐾𝐸 = ℎ𝑓 − 𝜙 Einstein in 1921 Nobel Prize portra Cited for PE Effect
  13. 13. Newtonian Physics Regular old classical physics When things get small Quantum physics When things get fast Special relativity Quantum field theory Small & fast

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