electrostatics - plainfield east high schoolpehs.psd202.org/documents/aseverin/1551379433.pdf ·...
TRANSCRIPT
1
•Electrostatics
is the study
of electric
charge at
rest. 2
What Is Static Electricity?
• A stationary electrical charge that is built up
on the surface of a material
3
Read Intro of Handout
• Charged Versus Uncharged Objects:
Compare number of e- to number of p+
• Positively-Charged
• Negatively-Charged
• Uncharged (neutral)
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p+ > e-
e- > p+
p+ = e-
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1) Contains Positive and Negative charges
2) The Negative charges moved to the top b/c they’re
attracted to the Positive bar.
3) The Positive Arm repels.
++++++++++++++
Don’t let electrons travel thru
Examples:
Wood
Plastic
Paper
Rubber
Grass
Let electrons travel thru
Examples:
Water
Metals: Cu, Al, Au
Salt Water
Alloy
Graphite
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q/Q Coulomb (C)
Electrons -1.6 x 10-19 C
Protons +1.6 x 10-19 C
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1C x 1e-/-1.6 x 10-19 = 6.25 x 1018 e-
Electrons transfer.
Electrons are the only ones
that can move.
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CHARGE BY FRICTION
PhET Sweater
Drag your
feet on the
carpet.
Rub balloon
on your
hair.
Electrons
are
transferred
from one
material to
another.
When a balloon rubs a piece of wool...
– electrons are pulled from
the wool to the balloon.
The balloon has more
electrons than usual.
+
+
+
+
+
–––––
The balloon: – charged,
The wool: +charged
wool
CHARGING BY FRICTION:
Rubbing materials does NOT create electric charges.
It just transfers electrons from one material to
the other.
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A balloon when rubbed on your
head becomes charged by picking
up extra electrons from your hair.
That same balloon, because it is
charged, will attract a neutral
object like pieces of paper.
-+
-
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11
CHARGE BY CONDUCTION
Requires
CONTACT.
Electrons transfer.
Both are left
Negative.
Charged object
touches a neutral
sphere.
During rubbing, what have been
transferred between the woolen cloth
and the balloon?
A Electrons B Protons
C Neutrons
A balloon has a negative charge when rubbed by woolen cloth.
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13
CHARGE BY INDUCTION
Negative object
moves near a
neutral sphere.
Just move close
to it – no contact.
Requires
grounding.
14
If the balloon can attract some paper
scraps, which of the following cannot
be the charge of paper scraps?
A Neutral B Positive
C Negative
A balloon has a negative charge when rubbed by a woollen cloth.
15
• In conducting objects, they are so loosely bound
that they may be induced into moving from one
portion of the object to another portion of the
object. To get an electron in a conducting object
to get up and go, all that must be done is to place a
charged object nearby the conducting object.
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17
CHARGE BY POLARIZATION
What effects will a charged balloon have on:*When Negative
Charge gets near the
e- freely move away
(repel) causing a
positive side to
attract
*Neutral particles
line up – once
polarized then the
can sticks.
*So the stream of
water attracts
*Can-Charged
Negative Balloon
to Pop Can
*Wall-Charged
Negative Balloon
to Paper
*Water- Water is
Polar
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In the context of electricity, polarization is the process of separating opposite charges within an object. The positive charge becomes separated from the negative charge. By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge. Charge becomes separated into opposites.
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Repulsion will be greatest for those electrons nearest negatively charged
balloon. Mass migration of electrons from balloon's side of aluminum can towards
the opposite side of the can. This electron movement leaves atoms on balloon's side
of can with shortage of electrons; they become positively charged.
Atoms on side opposite of can have an excess of electrons; they become negatively
charged. Two sides of aluminum pop can have opposite charges. Overall can is
electrically neutral; positive and negative charge has been separated from each
other. Charge in the can has been polarized.
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Grounding
• Removing the excess
charge on an object by
means of the transfer of
electrons between it and
another object of
substantial size.
• Example: Touch a door
handle and get shocked.
• Works because excess
electrons find each other
repulsive and forces them
to look for a way of
separating from each
other.
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Grounding
If the object has a positive charge...
Similarly, if the object has a negative charge...
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24
Which drawing shows the field around a single positive charge?
2. Which drawing shows the field around a single negative charge?
3. Which drawing shows an attraction?
4. Which drawing shows a repulsion?
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