Lecture 2010/19/05. wavelength Amplitude Node Electromagnetic Radiation (Light as waves) Moving...
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- Lecture 2010/19/05
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- wavelength Amplitude Node Electromagnetic Radiation (Light as waves) Moving Waves
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- c = c = speed of light (3 x 10 8 m/s in a vacuum) = wavelength (m) = frequency (s -1 or Hertz, Hz)
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- Electromagnetic Radiation Red light has = 700 nm. Calculate the frequency.
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- Standing (stationary) Waves Has 2 or more nodes Distance between nodes is /2. Distance between ends has to be n(/2)
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- 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?
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- 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?
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- 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?
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- 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
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- Photoelectric Effect
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- 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.
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- Photoelectric Effect E electron = E light - E ejection
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- Compare the energy of a mole of red light photons (= 700 nm) and a mole of UV photons (= 300 nm)
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- Dual Nature of Light Both wave and particle characteristics Wave Refraction Diffraction Particle Photoelectric effect
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- Diffraction Light bends as it moves through a slit or around a boundary
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- Refraction Bending of light as it passes between materials of different optical density.
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- Line Emission Spectrum Excited atoms emit light
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- Line Emission Spectrum
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- Balmer series Rydberg equation Balmer Series
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- 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
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- 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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- 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
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- 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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- Moving between energy levels
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- Calculate the wavelength of the green light of excited H atoms.