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Properties of Light Is Light a Wave or a Particle?

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Presentation on theme: "Properties of Light Is Light a Wave or a Particle?"— Presentation transcript:

1 Properties of Light Is Light a Wave or a Particle?

2 Bohr’s model of the hydrogen atom led to discussion about distinct spectra of light given off when it’s electron jumped from a higher to a lower energy level This discussion revolves around how to explain the behavior of light. Does it behave like a wave? A particle? Both?

3 Orbitals – places on the energy levels of the atom where electrons “hang out” Ground State – the lowest energy state of an atom Excited State – the energy state of an atom when an electron absorbs a specific amount of energy to move from a lower to a higher energy level

4 Wave Description of Light Electromagnetic Radiation – a form of energy that exhibits wavelike behavior as it travels through space Ex: Visible light, X rays, Ultraviolet, Radio waves, Gamma Waves Electromagnetic Spectrum – all types of energy that exhibit wavelike behavior

5 Electromagnetic Spectrum

6 Wavelength vs. Frequency Wavelength (λ) – the smallest distance between two repeating points on a wave λ is usually measured in meters (m), centimeters (cm) or nanometers (nm) ***NOTE: the visible light spectrum (ROYGBIV) is between 400-700 nm

7 Frequency (ν) – the number of waves that pass a given point per unit of time ν is usually measured is waves per second (1/s or s -1 ) or Hertz (Hz) All electromagnetic waves travel at the speed of light (c) c = 3.0 x 10 8 m/s

8 Frequency & wavelength are inversely related to one another. The mathematical equation used to describe the wavelike behavior of light is: c = λν

9 Practice Problem: Calculate the frequency of light that has a wavelength of 700.0 nm. What color of light is this?

10 Particle Description of Light Photoelectric Effect: electrons emitted from a metal when light shines on it. This phenomena could not be explained by the wave theory. Max Planck partially solved the issue by describing quantum.

11 Photoelectric Effect When light strikes a metal it release e- some of the time. There was a threshold energy that had to be met for the metal to release an electron. Planck stated that e- had a minimum energy that had to be met before they would start emitting light: quantum.



14 Quantum – light energy that is emitted or absorbed in small specific amounts Photon – a particle or packet of light carrying a specific quantum of energy German physicist, Max Planck, proposed the following mathematical relationship to determine the quantum of light given off or absorbed by electrons: E photon = hν

15 E = the quantum of energy given off or absorbed by electrons, measured in joules (J) h = Planck’s constant (6.626 x 10 -34 J  s) ν = frequency ( hertz or 1/s or s -1 )

16 Practice problem: Determine the energy in kilojoules of a photon whose frequency is 2.98 x 10 16 s -1

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