KitsGuru Transistor as a switch Educational Electronic Hobby Kit

One of the most common uses for transistors in an electronic circuit is as simple switches. In short, a transistor conducts current across the collector-emitter path only when a voltage is applied to the base. When no base voltage is present, the switch is off. ie no current can flow from collector to the emitter. In the given circuit we have used an LED in series with the collector and emitter so that whenever the current flows from collector to emitter, the LED glows. To provide a voltage at the base, we have used a momentary switch S2. Whever we press the switch S2, the Base of the transistor gets connected with the input power supply via a resistor R2. Here R2 is used to prevent excess current flow. Now as the base current starts flowing, the Collector and Emitter gets connected and a complete current path is provided and current starts flowing from collector to the emitter and obviously the LED gets turned on.