Page 28 - Electronics Starter Kit_EN

5.4 Circuit Explanation

When you touch the probes, the LED will light up.

So when you touch the probes, indeed you are making a resistor between 5V and the base of
the transistor (TR2),it will be in the Active Region because the IB(TR2) current is not enough to
make it in the saturation mode, so we will take the IC (TR2) current which is much higher to the
base of the transistor (TR1) through 10KΩ resistor.

5.5 Example Picture

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