Re: Fuses

[Glenn Knapp <kahuna@VCN.COM>]

At 04:10 PM 11/03/99 -0500, you wrote:
> In order to reinforce the understanding of current in circuits  I like to
have
> kids build a circuit in which there is a homemade fuse,  and
> then instruct them to keep adding more bulbs in parallel.   It's nice
> to have a fuse that fails with some drama,  but the best I've come up
> with is a piece of iron from a steel wool pad.  Before failure these
> often glow somewhat,  but they also seem to have the undesirable
> property of an increasingly high resistance as more bulbs are added,
> thus even with a suitable power supply rather than batteries,  the
> bulbs dim each time another is added and I must wave my
> hands about the fact that in your living room this doesn't happen.
> I'm curious to know if anyone has a suggestion for a better material,
> and also,  if anyone can comment on what is actually used in real
> fuses.  Obviously the melting point has to be right,  but from what I
> see in this circuit,  a real fuse must also have a low
> resistance.


Gary,

I do much the same thing as you - use some fibers from steel wool with a
parrallel circuit to which one can add additional light bulbs to increase
the load.  To make it more spectacular, tape the steel wool fibers to an
inflated balloon, then connect the ends to the circuit.  Whent the load
gets large enough the steel wool will ignite and pop the balloon.  I think
that it is a good way to drive home the idea about fuses.

Glenn