A network with a dependent source, terminals open

This is the circuit from the lecture, running. Change it and the answer changes with it:

• Click any component value to edit it, or drag components to rearrange.
• The wrench opens a step-by-step analysis — it chooses a reference node and writes the node equations. Leave its Domain on the DC operating point for this deck.
• The crosshairs probe reads a node voltage or a branch current, so you can check any intermediate result rather than only the final answer.

Probe $a$–$b$ for $V_{oc} = 3$ V, then probe across the $4\ \Omega$: $v_x = 6$ V, and the VCCS is carrying $0.25 v_x = 1.5$ A. Try deleting the dependent source and watch $V_{oc}$ move — it is not a spectator.