1. Physics and the Quantum Model
Light and Atomic Spectra

2. Particles and Waves Wave Model
Light consists of electromagnetic radiation
Travels at 3.0 x 108m/s
Amplitude
Wavelength λ
Frequency ν (hertz)
c = λν
Electromagnetic Waves

3. Electromagnetic Spectrum
Waves of varying wavelength and frequency
All traveling at the speed of light through space
As wavelength increases, frequency decreases
Let’s take a look!
And another look here!

4. Emission Spectrum of an Element
Elements emit light when electrons oscillate between energy levels
When emitted light is passed through a prism (emission spectrograph), an atomic emission spectrum is seen
Each line spectra corresponds to an exact frequency of light
Each element has it’s own emission spectrum Take a Look!
Element Spectra

5. The Quantum Concept and the Photoelectric Effect
Max Planck looked to explain why emission spectra are not continuous
Answer: energy changes in discrete units
The amount of radiant energy (E) absorbed or emitted by a body is proportional to the frequency of radiation
E = hν
h = Planck’s constant = x 10-34Js

6. Einstein Takes a Turn
Einstein returned to the idea of light as particles
Light is described as quanta of energy acting like particles
Light quanta are called photons
E = hν applies to energy of photons too

7. The Photoelectric Effect
Metals eject e- called photoelectrons when light shines on them
Einstein was able to explain this effect using his particle theory of light
While difficult to understand, we can determine basic relationships by studying the photoelectric effect

8. Quantum Mechanics
Louis DeBroglie derived an equation that described the wavelength of a moving particle:
All matter exhibits wavelike motion
Heisenberg uncertainty principle: cannot know exact velocity and position of a particle at the same time

9. Final Conclusions The study of light extends through many disciplines
We can study light because of what it does
We do not have a 100% clear description of light but through experimentation we know that…light is both wave and particle