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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
• Slide 18
• 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.
• Slide 22
• 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
• Slide 25
• Slide 26
• Moving between energy levels
• Slide 27
• Slide 28
• Slide 29
• Calculate the wavelength of the green light of excited H atoms.