Transcript Book Light
Book Light Circuit Diagram 2 - AAA Batteries Push Button Switch Light Emitting Diode LED Diode 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 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? 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. 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