Time college lecturers got out a bit more and got dose of the real world.

In theory everything is lovely.

In practice I challenge you to take ANY transformer you've got, and plot Input Current & Output Current from off-load, thru to full rated load in say 5% steps. From that you can calculate and plot a graph of efficiency to prove my point. Enjoy the experience. Then take the efficiency graph and tell your college that life in the real world is far from theory - so far that it's not even close!

For example... let's try to prove the theory of the International Ampere (you know Amps... it's that unit of measurement all of us use every day of our lives... so really we should try to prove the definition before we use it)...

Quote from my University Notes "That constant current which when flowing down two straight parallel conductors of infinite length and negligible cross section, separated by a distance of one meter in a vacuum, produces a force between them of 2 × 10-7 newtons per meter of length."

You get full marks for reciting this like a Parrot in your exam... but let's try to prove it...

1. You go down to your local store and ask for two drums of cable of infinite length and negligible cross-section... you lug them home...

2. You borrow the space shuttle and unravel them in the (supposed) vaccum of space from planet Earth out towards infinity.

3. When you've reached infinity, you join the far ends together and come home.

4. Then you hook up the wire to your PSU with a DVM in series switched to the famous "Newtons per Metre Length" setting on the dial.

5. Take a second DVM in series and switch it to Amps.

6. When DVM No.1 shows 2x10-7 Newtons the other should be showing 1.0000 Amps (assuming it's in calibration).

Worked when I tried it...