# Ideal Transformers and Lenz Law

1. Nov 10, 2012

### p75213

Hi,
Can somebody answer this question?

The induced magnetic field of the secondary coil opposes the magnetic field of the primary. Therefore there is a lower magnetic field on the primary - lower impedance and a lower voltage drop. This results in an increased primary current which will in turn increase the primary bemf and therefore the primary voltage will rise and so goes the cycle.

In the article I have read it says the increased primary current results in a larger power draw. I am wondering how can this be when at the same time the primary current is increasing the primary voltage is decreasing. It seems to me the power draw would be constant.

2. Nov 10, 2012

### Carl Pugh

They are talking about an instantaneous process. When calculating power the primary voltage can be considered constant.
The current increases with load and the voltage stays the same, so the power increases.

3. Nov 12, 2012

### p75213

Thanks for that