Download Book Light

Book Light
Circuit Diagram
2 - AAA
Batteries
Push Button
Switch
Light
Emitting
Diode
LED Diode
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Diode is a one-way electrical switch that
passes current in one direction.
The LED emits light of a certain
wavelength (i.e. color)
Constructed with a semiconductor material
A semiconductor is a material that in it pure
form does not conduct electricity well.
Silicon is a common semiconductor with four
electrons in its outer shell.
A silicon atom shares electrons with four
neighboring atoms allowing the outer shell to be
filled completely.
http://www.thenakedscientists.com
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By substituting some of the Silicon with atoms
that have five (instead of four) outer electrons,
there are electrons left over to roam
By substituting some of the Silicon with atoms
that have three outer electrons there are ‘holes’
created.
Negatively doped Silicon
Positively doped Silicon
P-type Dopant
N-type Dopant
Electrons and holes are pushed toward junction
when a positive voltage is applied to the P-side
At the junction, Electrons and Holes recombined
Energy in the form of light is given off
when an electron and hole combine.
A roaming electron has more energy than
an electron bound to an atom (in a hole).
That energy is given off as light.
Electrons and holes swept away from junction when a
negative voltage is applied to the P-side, so no current
flows in circuit
What makes the light white?
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LEDs usually emit one wavelength (color)
of light.
Most White LEDs use a blue LED (GaN)
covered with a yellow phosphor coating.
The yellow mixed with blue appears white.
A phosphor material emits light
when exposed to radiation. In this
case the phosphor is “excited” by
the blue light and in turn emits
yellow light.
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Pre-assessment #4
How does a LED and diode work?
Next two tests (review updated schedule)
Oral presentations
Book Report
Bring CDs and music sources (MP3s, etc.) on
Monday
Other motors (4-pole, reed switch)
Makes sure and pick up graded stuff
Get handouts
Speakers, recording sounds, transmitting data