Review
Big Idea #1?
Review
Big Idea #1?
Big Idea #2?
Review
Big Idea #1?
Big Idea #2?
Big Idea #3?
Question
Why is a charged object attracted to a
neutral object?
Question
Why is a charged object attracted to a
neutral object?
The neutral object gets ‘polarized’ which
makes the near side of the neutral object
appear ‘oppositely charged’ which will
attract the charged object
Polarization
Still Neutral but
the charges have
re-arranged
themselves.
Polarized
Balloon
Hand
Methods of Charging
Today’s Topics
Friction
Conduction
Induction
Charging by Friction
When 2 objects come in contact and move
past each other
– One material wants to give electrons
– The other wants to take electrons
Ex) Scuffing your feet on the carpet
Ex) Sliding out of your car seat
Charging by Friction
Fur/hair likes to give electrons
Silk likes to take electrons
Van De Graff Generator
Charging by Conduction
C
This is the physical touching of a charged
object to another object.
The electrons flow from a high
concentration to a low concentration.
A
B
Conduction Demo
The electrons went
from the stick to the
electroscope,
– Thus charging the
electroscope
negative.
– The object gets the
same charge as the
stick!
Conduction Question
Diagram what the electroscope charge
would be and how it became that charge
if the stick were charged positive?
Conduction Answer
The electroscope
would be charged
positive.
– Any electrons from
the electroscope
would go into the
stick.
– The electroscope
would lose electrons
which makes it
positive.
Charging by Induction
This involves polarization and
grounding.
– Polarization The rearranging of the
charges in a neutral object.
The net charge is still
neutral but the charges
have rearranged themselves
due to the presence of a
charged object.
– Grounding Attaching the object to the
earth where electrons are
free to enter or exit.
Induction Demo
The electrons in the electroscope want to get as far
away from the stick as possible (polarization),
When we grounded the electroscope,
– The electrons escaped thru the ground, leaving the electroscope
charged positive.
When charged by induction, the electroscope is left with
the opposite charge of the stick!
Induction Question
What charge would the electroscope be if
charged by induction with a positive stick?
Be able to explain how this happened.
Induction Answer
The electroscope would be charged
negative.
– The electrons would be drawn towards the
top of the electroscope.
– When grounded, more electrons would enter,
thus giving the electroscope a negative
charge.
Question
Why when you rub a balloon on your
sweater, it will then stick to the wall or
ceiling? After a long while it eventually
falls? Why?
Answer
The balloon gets charged
negative by friction.
When you put it on the wall it
polarizes the wall which
creates the attraction.
The balloon is an insulator so
it holds the charge for awhile
Eventually the negative
charges enter the wall and
neutralize the balloon and
falls.