Transformer efficiency.

[Nightwatchman]

Homework Statement

What is the the efficiency of a transformer with 13w of primary power.
120Vp, Np unknow
12Vs, 90Np

Homework Equations

The Attempt at a Solution

eff= Psec/ Pri * 100

Homework Statement

Homework Equations

The Attempt at a Solution

 

[rl.bhat]

120Vp, Np unknow
12Vs, 90Np
In first line you say Np is unknown and second line you say Np = 90. which is correct?