Rod Speed wrote:
The Natural Philosopher wrote
Rod Speed wrote
The Natural Philosopher wrote
MM wrote
Andy Dingley wrote
Adam Funk wrote

On a related note, is there a good & easy way to destroy data CDs? CDs or CD-ROMs?

If they're CD-ROMs, you can microwave them. You need to space them
apart if you're doing a batch (plastic toastrack, or else a $500
silicon wafer processing boat). You also need to do them for just
long enough to nuke the data layer, but without cooking the
plastic or there's a fume problem. For regular industrial use I
was able to use a cheap domestic microwave from Currys, but had
to mod it with a fixed timer and a single big push button.

CDs can't be nuked to reliably kill the data without getting them hot enough to cause a fume problem. Shredding is
easier, although you do need a hefty shredder.

I do not understand this penchant for microwaving CDs! Toxic, extremely obnoxious fumes will be released.

Absolute bull****.

Yes.

You simply dont understand: you are rapidly heating the conductive
metallisation which arcs and splits apart without even getting the plastic hot.

It uses the properties of the microwave to put heat into conductors,

No, in fact they just bounce off those. Thats why alfoil on the
ends of say chicken chicken drumsticks stops the ends burning.

Microwaves (to heat) need to get absorbed by something.

Yes, but the destruction of CDs when done right isnt done by heat.

They 'bounce off' thick metal film because they do get absorbed,

They bounce off thick metal film even when there is nothing to absorb them, like
when microwave is empty and you only have the thick metal walls etc there.

and that sets up currents that effectively cancel the EMF at that point this reflecting them back with if you like a
counteracting EMF generated by the foil.

That utterly mangles what actually happens.


No, its a valid mathematical way of looking at it actually - and the way
that explains WHY a conductor 'reflects' incident radiation.

In terms of a classical EMF model anyway. the same properties undergo a
transform into different equations in the quantum theory of photon
reflection.

But then you didn't do honours in electrical sciences, so you woudln't
probably have come across teh maths or that particular explanation.


Microwaves bounce around inside the microwave oven.

yes, and the reason why they do is because the walls are made of metal
that is thick enough not to smoke.


They dont get absorbed by the ends of the chicken drumsticks
that you have covered in foil just because they cant get thru the
foil and so whats under the foil doesnt get heated, and so doesnt
burn.

correct, but the waves DO get absorbed by the *foil* SURFACE ...and
that's what MAKES the foil SURFACE a microwave reflector.

It has circulating currents induced in it that set up an opposing EMF
that becomes the 'reflected wave'

That is why (in e classical model) reflection happens and not absorption
as it were, nevertheless nothing is a perfect reflector. The energy that
is lost - if its large enough, will heat the 'reflector' and destroy it.





You still get conduction of the heat thru the bone from the
part of the drumstick that isnt covered in foil and so is heated by
the microwaves.

BUT that current itself does heat the foil a bit

Nope.


Yes. Put a mirror in the sun. It still gets hot. Not as hot as a black
plate, but it gets hot.

Same for any reflector .


and if the foil is thin enough...

The reason you get a spectacular light show is the very thin foil getting
vaporised by the currents that flow in the foil because its an antenna.


if it absorbs no power than it wont - cant- get hot.

You are actually contradicting yourself Rod.


Nothing to do with heat.

so how do you vaporise metal without heat, Rod?

Theres a Nobel prize waitng for you

Its a bit like saying you want see a voltage drop across a straight
piece of metal - well you wont until you have a larger enough current
and a small enough piece of metal and then you have a fuse.

Cut thats current, not heat.

I squared R, Rod.


Do you have any basic knowledge of physics at all?

CD metallization is thin enough to not withstand the currents needed to reflect the microwaves without fusing - that's
all.

Yes, and its not heat, its currents.


Oh Rod...purlease.




--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.