Them!
Question: I have been amazed to see ants emerge seemingly unharmed after
being zapped in the microwave, usually after hitching a ride on my coffee cup.
They seem to run around quite happily while the microwave is on. How can they
survive this onslaught?
Answer: The answer is quite simple. In a conventional microwave, the waves
are spaced a certain distance apart, because that is all that is needed to cook
the food properly. The ants are so minute that they can dodge the rays and so
survive the ordeal.
Li Yan (age 12)
Advertisement
Norwich, Norfolk
Answer: The phenomenon that the ants take advantage of is that microwaves
form standing waves within the oven cavity.
So in some places in the oven space, the energy density is very high, whereas
in others it is very low. This is why most ovens have turntables to ensure that
cooking food is heated evenly throughout.
This standing wave pattern can be observed by putting a static tray of
marshmallows in the microwave, and heating for a while. The result will be a
pattern of cooked and uncooked marshmallows. The standing wave pattern, however,
varies according to the properties and position of any material within the oven,
such as a cup of water.
The ant will experience this pattern as hot or cold regions within the oven
and can thus locate the low-energy volumes. If the ant is in a high-field
region, its high surface area to volume ratio allows it to cool down more
quickly than a larger object while it searches for a cold spot.
It is a common myth that microwaves are too big to heat small objects. The
fallacy of this has been demonstrated by chemists such as myself who employ
microwave heating in their work. Certain types of catalyst consist of
microwave-absorbing particles鈥攖ypically of submicron size鈥攄ispersed
throughout an inert support material. There is convincing evidence that
microwaves are capable of heating only the tiny catalyst particles.
A. G. Whittaker
Heriot, Borders
Answer: There is very little microwave energy near the metallic floor or
walls of the oven. The electromagnetic fields of microwaves are 鈥渟horted鈥� by the
conducting metal, just as the amplitudes of waves in a skipping rope, swung by a
child at one end but tied to a post at the other, are reduced to nothing at the
post.
An ant crawling on the rope could ride out the motion near the post, but
might be thrown off nearer the middle.
For a quick demonstration of this, place two pats of butter in a microwave in
two polystyrene coffee cup bottoms, one resting on the floor, the other raised
on an inverted glass tumbler. Be sure to place a cup of water in the microwave
as well. On heating, the raised butter will melt long before the butter on the
floor.
Charles Sawyer
Camptonville, California
Dry run
Question: My late grandfather often talked about the 鈥淢iracle Bath鈥� sideshow
that he once saw at the Buffalo Bill Wild West Show early this century. Fully
clothed volunteers splashed about in a tank of liquid, apparently getting wet.
When they emerged, the 鈥渨ater鈥� simply ran off them, leaving them completely dry.
Can anyone explain how this effect was produced?
Answer: As a child I remember an excellent series of books outlining
experiments that could be done in the home using common household materials.
Many explored the phenomenon of surface tension in water, and how some
substances can alter it.
For example, soap reduces surface tension and helps wet greasy surfaces.
Conversely鈥攁nd this may be the secret of the Miracle Bath鈥擨 remember
that the books described how sprinkling a powder on water could increase the
surface tension to the extent that your hand could be immersed in the liquid
without breaking the surface and withdrawn still dry.
Clive Jervis
Southampton, Hampshire
The powder most commonly used in magical tricks of this kind is
lycopodium, a very fine powder consisting of spores of club mosses of the
genus Lycopodium. It is possible to coat your arm with the powder, plunge it
into water and stay dry.
Whether this was the actual method used in the sideshow we do not know.
Remember that lycopodium powder can be dangerous because it is so fine that it
can explode easily. But it is probably not as dangerous as the second
explanation for the magic bath given below鈥擡d
Answer: The Miracle Bath sounds as if someone was taking a bath in mercury.
Mercury resembles water when viewed from a short distance away, because it is
shiny and forms small puddles and droplets. I learnt this at the age of six
after trying to take the temperature of a candle flame. I played with the
mercury droplets from the broken thermometer for some hours鈥攏ot a practice
to be recommended.
The bath would not have had to be very deep because a human would float on
the surface very easily.
Of course, the reason you won鈥檛 see such a show today is that mercury is very
toxic and easily absorbed through the skin.
Cary O鈥橠onnell
Welwyn, Hertfordshire
This week鈥檚 questions
Rear lights: When I put a fresh disposable diaper on my daughter at night and
turn off the lights, the nappy lights up whenever she moves.
The light is very faint, like that produced by static electricity, and it is
a little hard to see but it is present. What is in the nappy that makes it do
this?
Andrea Jamison
Washington DC
Five live: Why do we have five fingers on each hand and five toes on each
foot?
Joe Baris Spring (aged 6)
Ankara, Turkey
No froth: I am a regular cappuccino maker and have noticed that sometimes it
is impossible to get the milk to froth. No matter how hard you try, some milk
stays dead. Fresh milk usually froths better, but even this doesn鈥檛 always work.
Why does some milk froth and other milk not?
Don Hadden
Vries, The Netherlands