Take the circuit from the last experiment and leave the potentiometers P1 and resistor R1 unaltered. You know that you have a very weak signal.
Build the circuit shown that now contains two transistors. If you re-connected the battery, the LED will light up brightly again!
This circuit is known as a "Darlington Pair".
Over the next three experiments, you take a look at another class of transistor applications.