Reactive circuits, working out voltage of a voltage source

Jony130

Joined Feb 17, 2009
5,127
From voltage divider.
And if I do not made any error the answer is
Vs = 80V * (1 + (R1||R2 + R4 )/R6) = 80V *(1 +30/20) = 80V*2.5 = 200V
 

Dodgydave

Joined Jun 22, 2012
8,677
You don't know the DC resistance of the inductor L2, so you can't find it.

If its a short circuit, it will form a voltage divider with the resistors R4,6 so it will be half of the supply voltage, which is 160V.
 

shteii01

Joined Feb 19, 2010
4,647
Assuming Vs is DC voltage source.

Steady state here means:
1) All capacitors are fully charged and act as open circuits.
2) All inductors are fully charged and act as short circuits.

Redraw the circuit, replace all capacitors with opens circuits, replaced all inductors with a piece of wire (short circuit).

It looks like you will have 80 volts across R6. Reduce the circuit to two resistors, R6 and R whatever. The two resistors form voltage divider. Formula for voltage divider has 4 variables, you know 3 of those variables (R6, 80 volts across R6, R whatever), solve for Vs.
 

Thread Starter

cakfef

Joined Jan 29, 2016
5
Thankyou good people :) Also on the same question how do I work out the power dissipation, Ive worked it out and got 512mV but don't know if its correct. Thanks
 

shteii01

Joined Feb 19, 2010
4,647
Thankyou good people :) Also on the same question how do I work out the power dissipation, Ive worked it out and got 512mV but don't know if its correct. Thanks
Power is measured in Watt. Why is your result in volts?

Power here is Voltage times Current.
P=VI
Since you don't know any of the currents, but you do know voltages and resistances, you can do a bit of manipulation:
V=IR
I=V/R
Therefore Power can be found by:
P=VI=V(V/R)=\(\frac{V^{2}}{R}\)

From the simplified circuit (the one with just two resistors, R6 and R whatever) work your way back to the full circuit with all the resistors. Find the voltages across each resistor and use the resistor values that were given to you in the problem description to find power dissipation of each resistor.

For example:
You already know that R6 is 20 kOhm, votage across R6 is 80 V.
So Power dissipated by R6 is then=80^2/20000=0.32 W
 
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