Lecture 2010/19/05. wavelength Amplitude Node Electromagnetic Radiation (Light as waves) Moving...

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Transcript of Lecture 2010/19/05. wavelength Amplitude Node Electromagnetic Radiation (Light as waves) Moving...

  • Slide 1
  • Lecture 2010/19/05
  • Slide 2
  • wavelength Amplitude Node Electromagnetic Radiation (Light as waves) Moving Waves
  • Slide 3
  • c = c = speed of light (3 x 10 8 m/s in a vacuum) = wavelength (m) = frequency (s -1 or Hertz, Hz)
  • Slide 4
  • Electromagnetic Radiation Red light has = 700 nm. Calculate the frequency.
  • Slide 5
  • Standing (stationary) Waves Has 2 or more nodes Distance between nodes is /2. Distance between ends has to be n(/2)
  • Slide 6
  • a)Draw a standing wave with 1 node. What is the wavelength of this wave? b)Draw a standing wave with 3 nodes between the ends. What is the wavelength? c)If the wavelength of the standing wave is 2.5 cm, how many waves fit within the boundaries? How many nodes?
  • Slide 7
  • Visible Light 1.Which color in the visible spectrum has the highest frequency? 2.Is the wavelength of x-rays longer or shorter than UV?
  • Slide 8
  • The frequency of radiation used in microwave ovens is 2.45 GHz (1 gigahertz is 10 9 s -1. What is the wavelength in nm of this radiation?
  • Slide 9
  • Light as particles Max Planck- Vibrations are quantized Plancks constant E=h = hc/ E = energy (J) h = Plancks constant 6.626 x 10 -34 J-s
  • Slide 10
  • Photoelectric Effect
  • Slide 11
  • Classical theory said that Energy of ejected electron should increase with increase in light intensity NOT OBSERVED No e - observed until light of a certain minimum E is used Number of e - ejected depends on light intensity. Light consists of particles called PHOTONS of discrete energy.
  • Slide 12
  • Photoelectric Effect E electron = E light - E ejection
  • Slide 13
  • Compare the energy of a mole of red light photons (= 700 nm) and a mole of UV photons (= 300 nm)
  • Slide 14
  • Dual Nature of Light Both wave and particle characteristics Wave Refraction Diffraction Particle Photoelectric effect
  • Slide 15
  • Diffraction Light bends as it moves through a slit or around a boundary
  • Slide 16
  • Refraction Bending of light as it passes between materials of different optical density.
  • Slide 17
  • Line Emission Spectrum Excited atoms emit light
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  • Line Emission Spectrum
  • Slide 19
  • Balmer series Rydberg equation Balmer Series
  • Slide 20
  • Atomic Spectra and Bohr 1.Any orbit should be possible and so is any energy. 2.But a charged particle moving in an electric field should emit energy. Electron would eventually run out of energy
  • Slide 21
  • Bohr New theory : New theory : Quantum or Wave Mechanics e- can only exist in certain discrete orbits e- can only exist in certain discrete orbits Stationary states Stationary states e- is restricted to QUANTIZED energy states. e- is restricted to QUANTIZED energy states.
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  • Slide 23
  • n= principal quantum number n is an integer n with the lowest possible energy is said to be in the ground state Electrons with higher energy than ground state are said to be in an excited state
  • Slide 24
  • Calculate the energies of n=1, n=2, and n=3 states of the hydrogen atom in J/atom. R = 1.097 x 10 7 m -1 h = 6.626 x 10 -34 J-s c = 2.998 x 10 8 m/s
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  • Slide 26
  • Moving between energy levels
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  • Slide 28
  • Slide 29
  • Calculate the wavelength of the green light of excited H atoms.