### substance | conductor | semiconductor:

Transistor
* Most transistors are kinds of triodes
  - have three connections
* Some transistors can work with much higher currents, or have much higher current gains, etc.
* act as electrical switches that direct electrons around electronic circuits.
* also allow power to go only in one direction
  - amplify the signal, but they use current insead of voltage to do it
* always have one round side and one flat side.
* amplify or switch electrical signals.
* are also essential parts of amplifier circuits and devices
  - at the heart of all modern computers
  - devices found in many electronic instruments, such as radios and televisions
* are electronic components
  - less sophisticated than neurons
  - located in cell phones
  - miniature electronic switches
  - much smaller than vacuum tubes, draw less power, and generate less heat
  - part of circuits
  - semiconductor devices
  - switches that control electron flow in a microchip, the brains of a computer
  - the building blocks of the microprocessor, which is the brain of the computer
* are the main component of the microchips used in computers
  - components of microprocessors
  - workhorses of integrated circuits
* can be plastic encapsulated.
* come in unipolar and bipolar configurations.
* control electrical signals in certain ways.
* have no moving parts and are turned on and off by electrical signals
  - two positions- on and off
  - the number of transistors on the chip
* make up logic gates.
* require only a small amount of electrical current to run powerful computers.
* serve as switches and amplifiers for electrical current.
* switch and modulate electronic current.
* work by currents flowing one direction through the gate.
+ Amplifier, History
  * Since the 1960s, most electronic amplifiers have been built with transistors. Transistors are lighter, cheaper, and more reliable.
+ Preamplifier: Electronic musical instruments :: Electronics :: Audio technology
  * Early preamplifiers used vacuum tubes. Since the 1960s, most electronic amplifiers have been built with transistors. Transistors are lighter, less expensive, and more reliable.
  * The transistor can be used for a variety of different things including amplifiers and digital switches for computer microprocessors. Some transistors are individually packaged, mainly so they can handle high power. Most are inside integrated circuits.

Silicon
* Most silicon has conductivity.
* Some silicon becomes conductors.
* includes atoms.
* is an element

### substance | conductor | silicon:

Amorphous silicon
* acts as a photo-diode that produces currents when exposed to exterior light.
* glassy form of silicon, one of the most common elements in the earth's crust.
* photodiodes for replacing degenerated photoreceptors in the human eye.
* relatively new material.

Crystalline silicon
* has a metallic grayish color
  - luster and grayish color
  - the same structure as diamond
  - vibrations which can be classified by wavevector and by branch
* is more expensive, than hydrogenated amorphous silicon.

Pure silicon
* can exist in a shiny dark grey crystalline form or as an amorphous powder.
* has few free electrons and is quite resistive.
* is manufactured for the electronics industry
  - needed for the computer chips and integrated circuits found in so many items
  - now of great importance in the electronics industry as a semiconductor
* poor electrical conductor at room temperature.

Transmission line
* are high-voltage power lines
  - the big ones that run from remote gas fields to urban centres
* can transport electricity with less loss at higher voltages.
* supply power to large numbers of customers and to large geographic areas.