04 Intro to Transistors

A transistor can switch a flow of electricity, just like a relay. But it's much more sensitive and versatile.

Fingertip Switching

Concept learned from this demonstration:
A transistor amplifies any changes in current
that you apply to its base. 

Your finger is conducting positive voltage to the base of the transistor. Even though your skin has a high resistance and there is only a trickle of voltage reaching the transistor, the transistor still responds. It isn't just switching the LED on and off; it is amplifying the current applied to its base.


If you have dry skin, you might have to lick your fingers before
touching the wires for the LED to light up.

The fingertip switching demo is safe if the electricity passes just through your finger. You won't even feel it because it's 12 volts DC from a power supply of 1 amp or less. But it's not a good idea to put the finger of one hand on one wire, and the finger of your other hand on the other wire.

All about NPN and PNP transistors
A transistor is a semiconductor, it conducts electricity, but not always and its internal resistance varies depending on the power that you apply to its base.