1. How an NPN Transistor Works
Collector
NPN
2N3904
Base
Emitter
The flat side faces up

2. Take Inventory of your Parts
You will need the following parts from your kit:
Breadboard
220 ohms resistor (red, red, brown, gold)
3300 ohms resistor (orange, orange, red, gold)
NPN Transistor
LED (light emitting diode)
9 volt battery lead
3 wires
9 volt battery
Pushbutton switch

3. Use this schematic to construct the experiment.
Build the Circuit
Use this schematic to construct the experiment.
220 Ohm
collector
base
3.3K Ohm +
emitter
9 volts -
Quick Check:
Your circuit should like this one.

4. Do the Experiment Connect the 9 volt battery.
Observe the brightness of the LED’s.
Press the pushbutton switch.
Observe and compare the brightness of the LED’s.
Release the pushbutton, both LED’s should turn off.
Troubleshooting:
If the LED’s do not light up, check to make sure they in correctly.
Check the battery. Does it have voltage?
Are there any breaks in the circuit?
Is the NPN in the right way?