1. The problem statement, all variables and given/known data To set-up an equation for the efficiency equation of single-phase toroidal transformer given the circuit with the following mesh equations (s*L1+R1)*I1 + (-s*M)*I2 = V1 (-s*M)*I1 + (s*L2+R2+RL)*I2 = 0 2. Relevant equations Efficiency equation(?), equation derived by The Electrician at thread https://www.physicsforums.com/threa...-parameter-i2-to-v1-non-ideal-updated.901475/. 3. The attempt at a solution We're not sure about this but is it not V2*I2*cos(theta2)/(V1*I1*cos(theta1)) or M*di2/dt*cos(theta2)/(V1*I1*cos(theta1))? Or should I include the hysteresis and eddy current losses? P.S. We're Applied Mathematics students, not EE, however we actually needed these for our research. Thanks in advance.