“The more or less consen-
sus explanation was that the
grape would work as an antenna,
and that would create a current
through the skin bridge that
would eventually heat it up and
create the plasma,” says Bianucci.
Through the sacrifice of untold
masses of grapes (and 12 micro-
waves), the researchers showed
that this hypothesis—which
had never been explained math-
ematically anyway—was false.
Not only is a skin bridge between
the grape halves not required, but
you can ignite a plasma fireball
in two whole grapes placed side
by side in a small bowl, or two
ground cherries, two quail eggs,
or even two hydrogel beads of
the type used in diapers.
Using microwaves with
the doors removed, “they
managed to decouple the
generation of the plasma—
the really f lashy thing you
see—from the actual phenomenon
that’s going on underneath, which
is the focusing of the electromag-
netic radiation, the microwaves,
in between the two spheres,”
Bianucci says.
It turns out that water-based
orbs about the size of a grape
amplify microwaves (which is
electromagnetic energy, just like
light) so effectively that a hot
spot just between the two orbs
creates plasma.
Apart from being cool, thisresearch may some-
day contribute to better
understanding of a field
called nanoplasmonics.
“If you put, for instance,
two metal nanopar ticles
next to each other, you have this
same effect, a really increased
electromagnetic field, but with the
metals you see it with light instead
of microwaves,” says Bianucci.
“The key thing is that the water
has a high ref lective index, so it
shrinks the wavelength a lot. If we
were able to find a material that
works like water, but for light,
where we could really shrink the
wavelength of light, then we could
probably use it to focus light into
very, very small spaces.”THE GRAPE
WOULD WORK
AS AN ANTENNA
THAT WOULD
CREATE A
CURRENT.“
More Experiments You Can Do With Your Microwave
If you’ve already
turned grapes
into plasma balls,
here are five other
things you can try,
according to Brad
Conrad, Ph.D.,
director of the
Society of Physics
Students.1 SOAP BUBBLE
Carve a small
notch in the
middle of a bar
of soap that has
moisturizer. Put
the soap in the
microwave, turn it
on, and a bubble
will grow out of
the notch, which
will become big
enough to fill the
entire microwave.
The microwave is
heating up water
and the molecules
inside the soap to
cause it to expand.5 EXPANDING
PEEPS Peeps or
other large marsh-
mallows expand
and explode in the
microwave. Put
them on a paper
plate, arrange six
to 10 Peeps in a
pyramid fashion,
and start the mi-
crowave. They will
slowly grow and
expand to three
to four times their
original volume.
When they cool
off, you can still
eat them.4 CD LIGHT SHOW
Put a glob of Silly
Putty on an edge
of a CD so the CD
can stand up in
the microwave.
Dim the lights in
the room, turn on
the microwave for
no more than a
few seconds, and
you’ll see colorful
flashes of light.
The CD—which
has a very thin
layer of met-
al—is reflecting
electromagnetic
radiation.3 SPEED OF
LIGHT Put a thin
layer of mini-
marshmallows on
a plate, and put it
in the microwave
(with turntable
removed) for 15
to 20 seconds.
Measure distance
between the
melted marshmal-
lows in centime-
ters. Calculate
the speed of light:
2 x (distance
between melted
spots) x (micro-
wave frequency).2 EXPLODING
EGG Place an egg
in the microwave,
and the egg will
explode. You will
also hear a loud
boom. Similar to
a popcorn kernel
popping, the
sound you hear
from the egg is
an explosion from
the water that
becomes present
when it’s heated.
Once the egg’s
shell cracks, it
expands rapidly,
hence the noise.November 2019 31