Krampf Experiment of the
Week - Squeaky Needle
http://www.krampf.com
Our second week of Florida Power and Light meetings went even better
than the first. In addition to getting lots of work done, we also
managed a trip out to Sanibel Island, to pick up some sea shells and
tour the Ding Darling Wildlife Refuge. While touring the refuge, I took
lots of video, including Rosy Spoonbills, Reddish Egrets, alligators,
and some marvelous lightning. Looking at the video later, I saw
something that I had not noticed while taping. In one frame when I was
photographing distant lightning, a streamer of spark about three feet
long can be seen leaping upwards from a nearby car. Luckily, this spark
did not connect to the lightning bolt, but it showed that the potential
was there for me to have a much closer experience with lightning.
This week's experiment is closely related to my close call with the
lightning. This week's experiment will give you an idea about why that
spark jumped upwards. You will need:
* your television
* a needle, pin or sharp nail
Turn on the television and bring the back of your hand near the screen.
You should feel the hairs on the back of your hand standing up. This
lets you know that there is a charge of static electricity on the
screen. This static charge will give us our squeak.
Pick up the needle and hold it as if you were going to stick something
with it. Bring the point of the needle close to the screen of your
television and listen carefully. You should hear a faint sound,
somewhere between a crackle and a squeak.
What is happening? Your television works by shooting a stream of
electrons at the tiny dots that make up your television screen. The
beam of electrons is moved about by powerful magnets, causing it to
"paint" the pictures you see on the screen. In the process, excess
electrons are left on the screen, giving is a strong, negative static
charge. As you brought the back of your hand near the screen, the
negative charge of the screen pushed electrons in the hairs of your
hand away, leaving these hairs with a positive charge. Since opposite
charges attract, the hairs stand up and are drawn towards the screen.
The same thing happens with the needle. Electrons are pushed away from
the point of the needle, leaving it with a strong, positive charge. The
point of the needle concentrates this charge to the point where it
begins to pull electrons out of the air. This flow of electrons through
the air forms tiny sparks which dance on the point of the needle. I had
hoped that these sparks would be visible if you turned off the
television and then moved the needle across the screen, but could not
get the room dark enough and my eyes adjusted to the darkness fast
enough to see the sparks. Though the sparks are not visible, they do
produce the squeaks that you hear coming from the needle.
Basically the same thing happened with my spark in the video. During a
storm, the clouds have a strong negative charge. This produces a
positive charge on the ground, just as the television screen did with
the back of your hand. This charge is particularly strong on tall
objects and points, just as it was on the needle. When the charge is
strong enough, it forms larger sparks that reach upwards. This spark
can reach upwards to connect with the descending spark, determining the
path that the lightning will take. Luckily, the lighting connected with
a spark from another place, not the one near me. Otherwise, I could
have had quite a shocking experience.