Objectives… To use LED lights to… – Understand how light is produced – Understand how LED...
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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
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
Slide 3
What do you know about light? What is light?
Slide 4
Different Forms of Light Incandescent light bulb (and Halogens)
Florescent lamps Neon lights LEDs All require Excited ELECTRONS
YIPPEEEEEE!!!
Slide 5
The Bohr Model of Hydrogen Neils Bohr came up with the idea of
electrons in fixed energy levels
Slide 6
LED Lights LED- Light-Emitting Diode Activity 1 Get to Know
Your LED Kit You have 10 minutes
Slide 7
Bohr Model Continued When electricity was passed through
Hydrogen Gas, it glowed. The spectra of color looked like
this:
Slide 8
Every Element Has Its Own Emission Spectra
Slide 9
Light is Caused by Excited Electrons
Slide 10
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.
Slide 11
The Electromagnetic Spectrum
Slide 12
Wave On a String
Slide 13
Activity 2 Measuring the Wavelengths of Light 20 minutes
Slide 14
Set Up
Slide 15
Activity 3 Finding the Voltage and Crunching the Numbers 15
minutes
Slide 16
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!
Slide 17
Valence Electrons 3 4 5 Si As Al
Slide 18
Silicon atom
Slide 19
Mobile Electrons and Holes? P N
Slide 20
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!
Slide 21
Periodic Properties Ga N P As Ultraviolet Green Infrared Bond
energy determines Band Gap Energy
Slide 22
Slide 23
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
Slide 24
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?