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Electrostatic Charge Polarization
Name: Rocklady
Status: student
Age: N/A
Location: N/A
Country: Great Britain
Date: N/A
Question:
What happens when you rub a balloon with wool and
hold it next to an object that is neutral - I am finishing a unit
on static electricity with my class and this question was asked.
Replies:
This is actually very interesting. This attraction occurs because of
two facts:
1. All objects, even those that are "neutral," are composed of many
particles that are electrically charged. When they are neutral, the
amounts of positive and negative charges are equal to each other, and
they are closely mixed together.
2. The force of electric attraction or repulsion gets weaker as you
move the charged objects apart.
When an object with a net electric charge is brought near an object with
zero net charge, the smaller charges making up the neutral object become
polarized. Let us say that the charged object has a positive charge.
Then the negative charges in the uncharged object will be attracted to
it and the positive charges in the uncharged object will be repelled
from it. So, the uncharged object will have a slight negative charge on
the side near the positively-charged object, and a slight positive
charge on the side opposite the positively-charged object. (The more
easily that charges can move in the uncharged object, the more complete
this polarization will be. Try bringing your charged balloon near an
empty aluminum soda can lying on its side. The aluminum is a good
conductor, so charges polarize within it easily, and you can get the can
to roll toward the balloon.)
Because the electric force is stronger at close distances and weaker at
long distances, the positively-charged object will attract the nearby
negative charges in the neutral object more strongly than it will repel
the more distant positive charges. So, the net force will be an
attraction.
Richard Barrans
Department of Physics and Astronomy
University of Wyoming
Hi Rocklady,
You have got a couple of cool things going on. When you rub a
balloon with wool, or your hair, you are transferring electrons to
the balloon. The balloon becomes negatively charged due to the
additional electrons and the wool or hair positively charged due
to the stripping of electrons. When you hold this balloon that is
now negatively charged, next to a neutral wall, charge polarization
takes place. In other words, since there are no free electrons to
move throughout the material, there is a rearrangement of the
positions of charges within the atoms and molecules themselves.
One side of the atom or molecule is induced to be more positive,
(or negative), than the opposite side. This realignment and
proximity of the balloon to the wall allows the balloon to
stick to the wall. This charge polarization does not last.
Once the balloon is removed, the molecules go back to their
usual positions.
A Nice explanation of his is in Paul Hewitt's, Conceptual Physics
in the chapter on Electrostatics; chapter 32 in the third edition.
Happy Science,
Martha Croll
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Update: June 2012
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