Transcript Static Electricity

Some Thought Questions:
Why do some TVs build up so much dust very quickly?
Why does saran wrap stick to your bowl when it is just
plastic and nothing more?
Why doesn’t your cell phone work in some elevators?
Static Electricity
Some upcoming concepts
Charge
Force
Electron
Proton
Friction
Conduction
Induction
Sheilding
Grounding
The 4 Fundamental Forces
Strong Nuclear Force – The force that is
involved in holding the nucleus of an atom
together
Electromagnetic Force – The force that exists
between charged particles
Weak Nuclear Force – The force involved in
nuclear decay
Gravity – The force that exists between any two
objects that have mass.
Static Electricity
Electrostatics is the part of physics that deals with the
interactions between unmoving charges.
Static: Unmoving
Electricity: Charges
Static Electricity: Unmoving Charges
An Electrostatic force is the force that exists
between two charged objects.
But where do we see these forces interacting?
Structure of the Atom
Helium Atom
Neutron
Electron
-Negative Charge
Proton
Nucleus of Atom
-Positive Charge
Charge Interaction: Unlike
Charges
Opposite Charges Attract
- -
+
+
+
+
+
- -
Charge Interaction: Like
Charges
Like charges REPEL each other
- -- -
+
++ + +
-
+
+ ++ +
Electrostatic Force
(Coulomb’s Law)
Coulomb’s Law states that
the stronger a charge is, the stronger the force is
between it and other charges, and
the bigger the separation between the charges,
the smaller the force.
Is there another force that acts just like Electrostatic Forces?
Universal Gravity
Other then the fact that charges don’t just attract, but repel as
well, they work the EXACT same way as masses and gravity!!
Ions
Most atoms have an equal amount of protons and
electrons. Because of this they are neutral (they have no
NET charge)
If an atom has too few electrons, it has a net positive
charge
If n atom has too many electrons, it has a net negative
charge.
These are called IONS.
Ions are NEVER created by moving or trading protons.
The only part of an atom that moves from place to place is
an electron.
Charged Atoms
Neutral Atom
Positive Ion
+
+
Lost an electron so it has a
net positive charge
Charged Atoms
Neutral Atom
Negative Ion
-
+
+
-
Gained an electron so it has
a net negative charge
How to Charge and Object
Friction: Charging two objects by rubbing them together.
One takes electrons from the other so one becomes
positive and one becomes negative
Examples of charging by friction?
Conduction
Conduction (Contact): Since charges like to spread out,
touching a charged object to a neutral or differently charged
object will transfer charge.
What are some examples
of charging by conduction?
Induction
Induction: Bringing a charged object near a neutral object
to induce a dipole in the neutral object.
NO TRANSFER OF CHARGE!!!!!
Induction
Before:
Induction
Induce an “Electric Dipole”
Also called polarization
The negative charges move away from the
negative sphere. REMEMER, the protons
don’t move!
Induction
Induced charge in both blocks when we separate them
Positive Block
Negative Block
Second Example
What will happen if a bring a very positively charged object
near another object?
+
+
+
+
+
+
+
+
Induction
+
+
+
+
+
+
+
+
The electrons move toward the positive object and a dipole
is still formed!
Neutral Objects
Using your knowledge about induction and dipoles, how
do you think Neutral Objects are affected by charged
objects?
They Attract!
Neutral objects are attracted
to charged objects
Review of Insulators and
Conductors
Conductor: Allows Electricity to
flow easily
- In a conductor, electrons will spread out so they
are as far apart from each other as possible
- Metals, water with dissolved materials in it
Insulator: Does NOT allow
electricity to flow easily
- Glass, rubber, plastic, wood, pure water
Charge Distribution
How does charge distribute itself on an
object?
•Charges spread out as much as they
can. (only happens on conductors)
•To make the forces equal everywhere,
charges will bunch up at corners.
Charge distribution
on a car
What should you do if a broken power
lands on top of your car?
Shielding
Static charge occupies only the outer
surface of a conductor; inside the
conductor the electric field is zero.
Electric Fields
The space around every electrical charge
Has both magnitude and direction, a vector
quantity
Exploring Electrical Fields
Lightning
Lightning on Science Joy Wagon