Why does current take a different path if the switch is open

Why does current take a different path if the switch is opened or closed?

Now wire a simple circuit with a single input source (the switch from Activity 3.2), a single gate (in this case an inverter, and a two LED outputs (with current limiting resistors). Wire one each of the LEDs to correspond to a) sinking and b) sourcing as in Figure 3.4. When placing LEDs in the circuit, note that the positive terminal corresponds to the longer of the two LE leads CC 330 Q WM switch 1 k2 Da O 330 Q Db Figure 3.4: Simple single input, single output inverting circuit.

Solution

when switch is closed

diode is forward biase

it means it is short circuited

current will flow in separetely loop

Vda = (330+1000)I

I1 = Vda/1330

12 = Vdb/330