How to calculate the scheme?

Question

Electronics

How to calculate the voltage drop across resistors R1 R2 and R3? Thanks

Answer 1

In the chain R1 - R2, which is a voltage divider, with the key S1 closed, a current of 12 / (2000 + 1000) \u003d 0.004 A will flow. The current into the gate can be neglected. Accordingly, between the ground and point G will be 1000 * 0.004 \u003d 4 V. With the key open, the potential of t.G will tend to zero.
Similarly, when the transistor is open, the potential t. D will tend to zero, and all current will flow through the resistance R2 and the LED HL1. And when closed - in t, D., will tend to 12 V minus the voltage drop across the LED by about 0.6-2 V. The potential of t.S in all cases will be zero.