The steps I have done so far are: 1. Found Vx by ignoring the 4 Vx and doing a mesh on the loop which gives me 0.5 for Vx 2. Short circuit Voc after this i'm stuck. Can someone solve this. My friend got -15v but i'm not sure if he's right. Either way i have to submit this quiz today so if -15v is wrong then i'm getting this question wrong. It would be helpful if someone walked me through the solution though. Thanks.
You can also solve it by realizing no current flows through the dependent source, so Vx is a voltage divider output. Then the dependent source makes its negative side 4*Vx lower than the voltage at Vx.
I am applying the definition of a voltage source: its positive side is X volts above its negative side, regardless of whether X is a constant or a function. Since this doesn't load Vx (as there is no current through the dependent source), you can conclude that Voc = Vx - 4Vx because the voltage at the dependent source's positive side is the dependent variable. Since the dependent voltage source is 4Vx volts, its lower side will be 4Vx volts lower than the positive side. Same answer, but different approach.
The dependent voltage source is open circuit therefore passes no current in this circuit, as tshuck says. So the 20k and 50k resistors form a simple potential divider, which gives Vx. The voltage of the dependent source is stated to be 4Vx so its negative end is 20 volts below the node (+5) to which it is coupled. I make Vx = +5 volts and Voc = -15 volts. So now you have tshuck's mathematical method and a physical circuit explanation to compare.
In other words, you couldn't solve it and so you just copied your friend's answer and submitted it as your own. What's your school's policy on academic integrity?