So, this is a demonstration of primary and secondary coils, a kind of very unusual, neat
demonstration which is going to require somebody with some musical ability because we have
a little Cassio keyboard here.
So, Jonathan is our musician for the day, Jonathan come in, let's see, I think it's
switched on.
Let's give us some simple little ditty here, so we can hear it, well, you know, I can't
play anything, so, wow, is that Tchaikovsky or Beethoven, anyway, it's great, terrific.
Okay, now, let's bring in a coil here, if you look over here, Alex why don't you hook
this up.
Let's hook up a coil to this, it's just a straightforward coil, let's hook it in.
I don't have any musical abilities, so I'm just hooking up the gears.
No, no, you're the technical physics help here, okay, so you can see that, so just switch
it off, yes, switch it off, and we're going to produce a current now, we're going to play
and produce a current that goes into this coil, so listen carefully, okay, now Alex
has got some device on here, Alex you should be over way out in the wings here, can you
go back, okay, Alex wasn't following the script there, can you play it again now, okay, now
nothing, right, absolutely nothing, you sure you played it there, great, okay, now Alex,
what happened here was we produced a current in here, but of course nothing happened,
you can't hear a current, right, so Alex has got a secondary coil he's going to bring
in, and he's not going to touch it to this, you're going to lay it near the first one,
and attach to this secondary coil, there's a speaker, okay, so we're going to put the
speaker on the table here, and there's a circuit here, there's two wires coming in here, they
go at the speaker, and just to make sure there's no trickery here, I'm going to put a piece
of wood here, so now Jonathan's going to, in a second, is going to play the tune again,
it's going to produce a current in the primary, the primary current is going to produce a
B field through here, right through the wood, and the secondary is going to pick it up,
and then that current in the secondary is going to go through the speaker, and if everything
works and hold your breath, we're going to hear this masterpiece through this speaker,
do you believe this stuff? Okay, let's go for it then, okay, very good, and that was
coming through this speaker, right, now let's play with this little bit, so the strength
of the signal here depends on the coupling, so let's keep the microphone here, but while
it's playing, Alex is going to move the secondary back, which means the amount of field getting
into the secondary is going to go down, and so this should get less distinct, okay, so
now we're going to play through the secondary here, so Jonathan can you play again now,
and Alex is going to bring the coil back and listen to the sound, okay, so it's all a question
of the coupling, as the coupling gets stronger, the sound gets louder, and as the coupling
gets weaker, the sound gets weaker, now there's one last thing we can try, as we said, the
key thing is the coupling between the primary and the secondary, so if we can increase that,
we get more sound, so Alex has a very heavy iron bar here, which he's going to maneuver
in the center, and that of course helps the flux to go from here to here because the beefiel
likes to go in the iron bar, and as he maneuvers it into the center here, and Jonathan's playing,
we should hear the sound go up, okay, I'm going to put the speaker behind here so we
can see it, and okay, why don't we start here, and then you'll have to move these apart
a bit, push the bar in and sort of push them together, and let's listen to the sound, right,
it should go up, that's the idea, okay, go ahead, now, it's even louder, right, and weaker,
so the iron bar, so let's just stop for a second, okay, let's play it there without
the iron bar, play it, kind of not so loud, right, I'm going to mark the distance, now
put the iron bar in, pop it in there, same distance, let's kind of put it equally spaced,
now play it again if you would Jonathan, okay, huge effect, right, very good, yep, good job
guys, thanks a lot.
