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Objectives…

Objectives…. To use LED lights to… Understand how light is produced Understand how LED lights work Calculate wavelengths of light Calculate frequencies of light Measure voltage and convert it to energy Calculate Planck’s Constant

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Objectives…

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  1. Objectives… • To use LED lights to… • Understand how light is produced • Understand how LED lights work • Calculate wavelengths of light • Calculate frequencies of light • Measure voltage and convert it to energy • Calculate Planck’s Constant • Understand basics of Quantum Theory and how it relates to light

  2. What do you know about light? What is light?

  3. Different Forms of Light • Incandescent light bulb (and Halogens) • Florescent lamps • Neon lights • LED’s All require “Excited ELECTRONS” YIPPEEEEEE!!!

  4. The Bohr Model of Hydrogen • Neils Bohr came up with the idea of electrons in “fixed energy levels”

  5. LED Lights • LED- “Light-Emitting Diode” • Activity 1 “Get to Know Your LED Kit” • You have 10 minutes…

  6. Bohr Model Continued… • When electricity was passed through Hydrogen Gas, it glowed. The spectra of color looked like this:

  7. Every Element Has It’s Own Emission Spectra

  8. Light is Caused by Excited Electrons

  9. What Bohr Concluded… • As the electrons absorb energy they become “excited” and move to a higher energy level • When the electrons move back to the original “ground state,” the energy absorbed is released as a photon of light • The color of light corresponds to a particular wavelength and frequency and therefore a specific, discrete amount of energy released. A photon is a “quanta” of energy because it occurs in specific, discrete amounts. Hence the term, “Quantum Model” of an atom. photon emitted Photon emitted

  10. The Electromagnetic Spectrum

  11. Wave On a String

  12. Activity 2Measuring the Wavelengths of Light20 minutes

  13. Set Up

  14. Activity 3Finding the Voltage and Crunching the Numbers15 minutes

  15. What About Light from an LED? • Made mostly of semiconductor elements • The Group 14 elements are the Key! • Light is still caused by EXCITED ELECTRONS!

  16. Valence Electrons 3 4 5 • • • • Si Al As • • • • • • • •

  17. Silicon atom

  18. Mobile Electrons and Holes? N P

  19. Band Gap Energy • The Energy of “Excited Mobile Electrons.” • As the Excited Mobile Electrons “fall into ground state holes” that energy is released as photons of light!

  20. Periodic Properties Ga N Ultraviolet Ga P Green Ga As Infrared Bond energy determines Band Gap Energy

  21. LED Data Table

  22. Max PlanckThe Father of Quantum Physics Energy = Planck’s constant x wavelength h = 6.626 x 10-34 J•s Does this number look familiar?

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