Day Four: Transistor Switching

A transistor can switch the flow of electricity just like a relay but it's more sensitive and versatile. We are using one 2N3904 transistor for this experiment.

Transistor Switching
I removed the 10kΩ resistor, and replaced with two wires. I then touch the tip of my finger to the two wires. The wires are not touching each other, but my finger is conducting positive voltage to the base of the transistor. It lights up the LED.
 

Transistor Switching continued
I lick the tips of my fingers and the LED glows more brightly because
a transistor amplifies any changes in current that you apply to its base.

All about NPN and PNP transistors
A transistor is a semiconductor, meaning that it does not always conduct electricity. Its internal resistance varies depending on the power that you apply to its base. NPN and PNP are bi-polar semiconductors. They conduct using both polarities of carriers - holes and electrons.

• All bi-polar transistors have three connections:
  Collector (C), Base (B), and Emitter (E).
• NPN transistors are activated by positive voltage
  on the base relative to the emitter.
• PNP transistors are activated by negative voltage
  on the base relative to the emitter.