Re: Ideal transformer

["Bob Sciamanda" <trebor@velocity.net>]

2nd transmission - first appears to have died en-route

An IDEAL transformer with open secondary will draw no primary current.
This is due to the ideal primary properties of zero resistance and
infinite SELF inductance.  Your doorbell transformer primary is
permanently connected to the power mains; the push button switch is in
the secondary.  It is not ideal; it gets warm and you do pay some
idle-running costs.  (I might add that even if the self inductance is
finite , if the resistance is zero then no net power is consumed over a
cycle - except for heating of connecting wires by the reactive current.)

-Bob

Bob Sciamanda   trebor@velocity.net
Dept of Physics
Edinboro Univ of PA  http://www.velocity.net/~trebor
Edinboro, PA   (814)838-7185
-----Original Message-----
From: Ken Fox <kfox@stega.smoky.org>
To: Physics List <phys-l@atlantis.uwf.edu>
Date: Wednesday, April 29, 1998 11:14 PM


> A friend frowarded this question to me from a 1996 IB Physics exam. I am
> unsure how to reply to c.
>
> Any quick insights. I have some thoughts but would rather not risk the
> flames ;-). or prejudice your replies.
>
> In an ideal transformer the input is 12V 24W when connected to a
> > load and it has 100 turns. The output is 240V. Determine:
> >       a) the number of secondary turns -
> >       b) value of current in the secondary coil -
> >       c) power in the primary when the output is not connected to any
> >               resistance -
> >
> >       My Answers for the transformer ? I'm troubled with (c) question.
> >
> >       a) 2000 turns
> >       b) 0.1 A
> >       c)
>
>
> Ken Fox
> Smoky Hill High School
> 16100 Smoky Hill Rd
> Aurora,CO 80015
> 303-693-1700(w)
> 303-850-7537(H)
> kfox@stega.smoky.org