# Homework Help: Ideal Transformer

1. May 15, 2006

### noobish

something i read from the text book and i don't understand.

"in an ideal transformer, no magnetizing current is required to produce the flux"

so, where does the flux come from?

2. May 15, 2006

### Andrew Mason

If the secondary is open there is no power drawn from the power source. But there is current in the primary. The current in the primary is the cause and result of the buildup and collapsing of the magnetic field in the primary (it is self perpetuating).

If the primary coil is a perfect inductor (in an ideal transformer R = 0) the current lags the voltage by 90 degrees. Since Power is $VIcos\phi = VIcos90 = 0$ the currrent does no work.

AM

Last edited: May 15, 2006
3. May 18, 2006

### noobish

TQVM. i think i understand it already.

Last edited: May 18, 2006