Experiment 3 - The NPN-Transistor III

To understand how a transistor switches through, you need to take a closer look at the circuit and understand how currents flow. For this purpose you take an interim step in this experiment.

In the circuit shown, you recognize the pushbutton switch S1 and the resistors R1 and R2 from the last experiment. However, you now have added light emitting diode LED1.

Circuit. (Enlarge) After you connect the battery and push the pushbutton switch S1, the LED remains dark. The resistors R1 and R2 limit the current so significally that it is no longer sufficient for the LED to light up.

Circuit diagram.

What does this have to do with a transistor? In the next experiment, you bring back the transistor into the circuit.