Basically, in previous experiments you have used the transistor in a switch circuit. To illustrate this, expand the circuit from the experiment 2 by a potentiometer.
When turning the potentiometer P1, the LED lights up very brightly for a long time before she goes out relatively quickly. A small base current/b> is sufficient to fully switch through the transistor. If the base current decreases below a certain level, the transistor shuts rapidly.
The circuit shown is also known as a common emitter circuit. Wherever a transistor is used as a switch, this circuit is applied.
What is the difference to an amplifier?