Re: [Phys-L] Lenz's law and conservation of energy

[Bernard Cleyet <bernard@cleyet.org>]

On 2014, Apr 01, , at 10:47, John Denker <jsd@av8n.com> wrote:

> We drive the primary with a current, with a sinusoidal
> waveform.  Let the secondary be open-circuited at this 
> stage of the game.
>
> There will be some voltage across the primary, which
> we can calculate based on the primary current and the
> self-inductance.  So far so good.


This is something that has puzzled me since I first noticed a v. long time ago.

The drop from OC E/q  to loaded w/ a rather high resistance is not explained by the internal resistance and the external resistance load.  i.e. the E/q is > predicted by the input E/q and the turns ratio.  

bc confused?  


> Now .... short-circuit the secondary.  This means that
> the secondary voltage is now smaller than it was in
> the open-circuit case.  This in turn tells us that 
> there is less flux_dot threading the secondary.  This 
> means that the induced current in the secondary is 
> oriented /opposite/ to whatever flux the primary is 
> trying to push through the secondary.  


This is similar to back EMF (incorrect term now-a-days?)  in a motor?