How it works
The circuit uses a potential divider to feed a voltage into the base of the transistor. The middle resistor in the potential divider is a variable resistor, which allows the voltage to be adjusted from around 0.6 volts to 1.5 volts. The characteristics of transistors are such that they don’t change from being off to on instantly as the voltage changes. Instead there is part of their operation at the point where they begin to turn on where the amount of current flowing through the collector to the emitter can be controlled. By using the three resistors in the way they are connected we make use of this feature to limit the current flow and therefore the brightness of the bulb.
Parts List:
- 2-AA battery cage, with flying leads (stock code 2232-25 - packs of 25)
- 1K ohm resistor (stock code 3003-1k - pack of 100)
- 680K ohm resistor (stock code 3003-680K pack of 100)
- 1K Potentiometer (stock code 3002-1k)
- Transistor BC337-25 (stock code 2938 - pack of 50)
- Bulb holder (stock code 3517 - pack of 50)
- 3.5V bulb (stock code - pack of 50)
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