Q:

Voltage and current in this schematic

I'd like to understand this simple schematic to see if I get things clearly

If I understand things correctly:

when the switch is open, the current at the right black point is zero, the voltage is 12V.
when the switch is closed, the current at the right black point is 20 mA, the voltage is 0V

If this is correct, suppose now a similar schema with the following difference: between the switch and ground I have another 600 ohm resistor.

the potential at the black dot with the closed switch is now 6 V ?
any point along the horizontal connection between the T junction and the black dot are at the same potential. I guess they also enjoy the same current. If two points in a circuit experience the same potential and they are directly connected, do they always experience the same current as well ?

A:

(In ideal conditions)
You're correct in your understanding of the first case. When you close the switch, you short one end of the resistor to ground, so there's a 12V drop across it and I=0.02A.
In your second case, with the switch closed, you are creating a voltage divider so the point between the resistors is at 6V.
If you don't have a load connected along Vout (between the black dot and ground), then I=0 there since there isn't a voltage drop along the horizontal connection.
Measuring along the path connecting the resistors/switch, you'll see your 0.01A, and since there is no other path for the current to take, both resistors will see the full 0.01A.

