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Published byPaloma Manifold Modified over 6 years ago

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Niels Bohr in 1913 proposed a quantum model for the hydrogen atom which correctly predicted the frequencies of the lines (colors) in hydrogen’s atomic emissions spectrum.

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His model gave atoms only certain allowable energy states. The lowest state is called the ground state. When an atom gains energy it is said to be in an excited state.

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When elements are given energy from a variety of sources (heat, light, electricity) the electrons absorb that energy, & jump up to a higher energy level, the excited state. The electrons can return to ground state by giving off the energy as a color of light, called photons of light. Each element gives off a unique color called its atomic emission spectrum. The electrons are what give each element their unique color.

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Light gives us a clue to how electrons are arranged. Light behaves like a wave & like a particle. wave particle duality of nature – everything in the universe has properties of both waves and particles (ex. Duality of good vs. evil in man)

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Light in wave form is called an electromagnetic wave and is part of the electromagnetic spectrum which includes x-rays, TV waves, microwaves, radio waves, UV waves & gamma rays.

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Trough – low pointsCrest – high points Wavelength – the shortest distance between points in which a wave repeats itself. (crest to crest or trough to trough) symbol - λ Amplitude – max displacement from equilibrium (middle of wave).

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Rope demo

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Parts of a Wave Wavelength - of one wave, from a crest to a crest or trough to a trough Symbol = λ ( ) Measured in Frequency- number of waves that pass a point in 1 second symbol = f or v ( ) Measured in (Hz) or 1/s, s -1 length lambda meters nu Hertz

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Formula: c = λ v or Formula: c = λ f c is constant speed of light ν or f is frequency λ is wavelength All EM radiation travels at the speed of light, c = 3.00 x 10 8 m/s in the vacuum of space

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Ex. 1) Light in the middle of the ultraviolet region of the electromagnetic radiation spectrum has a frequency of 2.73x10 16 s -1. Find the UV light’s wavelength.

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Ex. 2) Yellow light has a wavelength of 5.70x10 -7 m. Calculate the frequency of the yellow light.

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Light as a particle is called a photon. Light is like a particle because there are only certain amounts of energy it can have. The minimum amount of energy a photon can have is called a quantum.

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Max Planck found that this energy could be calculated with the formula E = h ν or E = h f Once the minimum amount of energy is calculated, the actual energy can be a multiple of the quantum amount. (1x E, or 2 x E, or 3 x E....) v or f is frequency (Hz or 1/s or s -1 ) same frequency as earlier h is Planck’s Constant = 6.626 x 10 -34 Js E is energy, measured in Joules (J)

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Ex. 3 From examples 1 and 2, we have the frequency of UV light as 2.73x10 16 s -1 and the frequency of yellow light as 5.26x10 14 Hz. Calculate the energy in joules, of an individual photon of each.

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UV light(6.626x10 -34 Js)(2.73x10 16 s -1 ) =1.81x10 -17 J yellow light(6.626x10 -34 Js)(5.26x10 14 s -1 ) =3.49x10 -19 J Which has more energy? UV light or yellow light?

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Ex. 3 From examples 1 and 2, we have the frequency of UV light as 2.73x10 16 s -1 and the frequency of yellow light as 5.26x10 14 Hz. Calculate the energy in joules, of an individual photon of each. UV light(6.626x10 -34 Js)(2.73x10 16 s -1 ) =1.81x10 -17 J yellow light(6.626x10 -34 Js)(5.26x10 14 s -1 ) =3.49x10 -19 J Comparing the two, UV light has more energy than yellow light

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Electrons (called photoelectrons) are emitted from a metal’s surface when light of a certain frequency shines on the surface. Example: calculators. Photoelectric cells convert light into electric energy

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In Summary c = λ f or c = λ v c = speed of light = 3.00 x 10 8 m/s f (or v) = frequency = Hz, 1/s, s -1 λ = wavelength = m E = h f (or E = h ν ) E = Energy = J h = Planck’s Constant = 6.626 x 10 -34 Js

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Water drops in the air disperse the white light of the sun into a rainbow. What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 10 14 Hz?

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