Electricity: Getting a
CHARGE Out of It
Today's Snack: Snap! Crackle! Pop!
That's what electricity sounds like, when electrical charges collide. Since
we're working with charges today, let's have the perfect snack: a nice bowl of
Rice Krispies. Pour on the milk and hear those electrons dancing about!
Puffed rice cereal
4" square piece of tissue paper
Lid from a metal (preferably tin)
can, clean and dry (take care not to cut yourself)
Hard rubber comb
Another piece of tissue paper
Salt and pepper
The world revolves around the atom,
the smallest unit of measurement that we have, and within it, the eentsy
weentsy electron. Did you know that everything is always moving? Not just that
things are hyper, like when you can't pay attention in class. It's that
everything is composed of atoms, and atoms have electrons, which are always
moving. Nature is based on electricity, you see.
But everything isn't jolting around
all the time because of electromagnetic force. That's what controls the space
within atoms, acting as a sort of "glue" to keep electrons and protons in
place. EXCEPT . . . electromagnetic force does carry an electrical charge. A
"charge" is a property within all of our elementary particles of matter that
gives rise to all kinds of motions and interactions.
Within an atom, there will be a
proton with a positive charge (you can remember that because of the "pro" in
"proton" - and an electron with a negative charge. They're opposites, and they
attract. So if you put a positive proton next to a negative electron, they're
going to stick together. Meanwhile, if you put a negative electron next to
another negative electron, they're going to want to stay apart. That's called
"repulsion." It's the same thing you do when you see something gross, that
makes you sick, like your little brother's messy room - just kidding.
Anyway, electromagnetic force is
stronger than gravity and has a ton to do with what goes on in your everyday
life. Since atoms stick together and form molecules by sharing electrons with
each other, we experience massive amounts of electromagnetic force in every
molecule of our being, and our world, every moment of every day. Ironically, we
aren't even usually aware of it.
But we can do these fun experiments
to see electron transfer up close and personal. They're fun, so we'll get a . .
. CHARGE out of it!
Shooting Puffed Rice
Charge a plastic spoon by rubbing a piece of woolen cloth over it several
times. Hold it over a dish containing puffed rice cereal. The
cereal puffs jump up and remain hanging on the spoon, until suddenly they shoot
wildly in all directions.
What happens? The puffed rice grains are attracted to the negatively-charged
spoon and cling for a time. Some of the electrons pass from the spoon and
have the same charge. Because like charges repel one another, the puffed rice
grains fly away from the spoon.
Cut a spiral -shaped coil from a thin piece of tissue paper, about 4 inches
square. Lay it on a tin lid. Bend the center of the coil -- its "head" --
upward. Rub a fountain pen vigorously with wool cloth. Hold the pen over
the coil. It rises, like a living snake, and reaches upwards. See what
happens when the paper touches the pen.
What happens? In this case, the pen has taken electrons from the woolen cloth
and attracts the uncharged paper. On contact, the paper falls, because it
takes part of the negative electric charge in the pen and gives it up
immediately to the metal lid, which is a good conductor. Since the paper
is now uncharged again, it is again attracted upwards until the fountain pen
has lost its charge.
woolen cloth briskly back and forth along both sides of the comb. Tear another
piece of tissue paper into little pieces. The comb will "pick them up." You can
re-charge the comb and "pick up" ping-pong balls or a blown-up balloon. Now tell
your friends that you can make an inside-out salt and pepper shaker. sprinkle
salt and pepper on a plate so that they are not clumping up, re-charge your
comb very well, and then hold it one inch above the plate. The pepper will leap
onto the comb - but the salt won't move.
happens: The comb has been made negatively-charged by rubbing it with the wool,
so when it approaches the paper, ping-pong balls or balloon, the electrons
within these "neutral" objects retreat away from the negatively-charged comb.
So the edges of these objects shift over from "neutral" to positive charges,
making them attracted by the negatively-charged paper. Why did the pepper
"jump" but not the salt? Because the pepper is lighter in weight than the salt,
and could overcome the force of gravity more easily. Note: if you touch your
negatively-charged comb to these objects, or rub them to get them to be
negatively charged, too, you will see that they will suddenly repel the comb,
because the interaction is no longer "opposites attract."