Ideal Transformer Question

Thread Starter


Joined Sep 17, 2012
So for part A, I have an ideal transformer connected to a couple resistors.

*All voltages and currents I am assuming are rms in the problem because i don't want to type RMS for each one.*

a) So I did a source transformation to make the current source into a voltage source.
So \(V_{th}= 240<0 [mV] \)
Since I did a source transformation:
\( R_{th}=5+15=20 [k\Omega]\)

So i know in order to get the max amount of power from the load I have to make the source see a 20 [kΩ] through the number of turns in the coils. I am not 100% on how to do that (Find N2)?

b) That is just a voltage divider so I get \( P= V^2/R \)
\(P= (120)^2/20 = 720 [mW] \)

c) The voltage before the inductors and load is 120 V so if i put V2 across N2 then I have \(V_1+V_2=120 [V] \), also the voltage per turn is the same so but with dot convention they are opposites
\( V_1/N1=-V_2/N2
V_2=-(N2/N1)*V_1 \)
Putting that back into first equation

\(V_1-(N2/N1)V_1 = 120 \) (Solve for V1 which will give me V2)

d) Putting the circuit back to its original form before source transformation, I need to find the voltage across the source
KVL gives me \( V_{cs} = 120V + (240/40000)*5000 = 150 [V] \)
(240 [V] /40000 [Ω]) [<-- current before transformation back]
So \( P_{cs} = 150 * 10^-3 = 2.4 [W] \)
\( % = (.72/2.4)*(100)= 30% \)
So I just need to know how to find N2. I have been given a formula sheet which does not seem to help and we have not gone over this in class yet but my homework is due next tuesday and I am interested on how to solve for this.

Thanks for the help and time


Last edited:


Joined Mar 6, 2009
The winding voltages must be directly proportional to their individual number of turns as you have already indicated. What is the voltage V2? If you know a certain number of turns gives you voltage V1 (for which you have developed an equation) then a commensurate number of turns will give voltage V2.