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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 Plancks Constant Understand basics of Quantum Theory and how it relates to light

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What do you know about light? What is light?

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Different Forms of Light Incandescent light bulb (and Halogens) Florescent lamps Neon lights LEDs All require Excited ELECTRONS YIPPEEEEEE!!!

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The Bohr Model of Hydrogen Neils Bohr came up with the idea of electrons in fixed energy levels

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LED Lights LED- Light-Emitting Diode Activity 1 Get to Know Your LED Kit You have 10 minutes

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

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Every Element Has Its Own Emission Spectra

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Light is Caused by Excited Electrons

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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. Photon emitted photon emitted A photon is a quanta of energy because it occurs in specific, discrete amounts. Hence the term, Quantum Model of an atom.

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The Electromagnetic Spectrum

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Wave On a String

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Activity 2 Measuring the Wavelengths of Light 20 minutes

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Set Up

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Activity 3 Finding the Voltage and Crunching the Numbers 15 minutes

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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!

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Valence Electrons 3 4 5 Si As Al

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Silicon atom

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Mobile Electrons and Holes? P N

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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!

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

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LED Data Table Color Actual Wavelength (nm) Voltage (V) Frequency (1/s or Hz) Energy (J) Energy Divided by Frequency (Js) INFRARED9901.121 3.o x 10 14 1.8 x 10 -19 6.0 x 10 -34 RED 6601.831 4.5 x 10 14 2.9 x 10 -19 6.5 x 10 -34 ORANGE 620 1.8654.8 x 10 14 2.9 x 10 -19 5.9 x 10 -34 YELLOW 5901.898 5.1 x 10 14 3.0 x 10 -19 5.9 x 10 -34 GREEN 570 2.036 5.3 x 10 14 3.3 x 10 -19 6.1 x 10 -34 BLUE 4303.348 7.0 x 10 14 5.4 x 10 -19 7.6 x 10 -34

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Max Planck The Father of Quantum Physics Energy = Plancks constant x wavelength h = 6.626 x 10 -34 J s Does this number look familiar?