Transcript Coulomb’s Law

Electrostatics
• Electrostatics is the study of
electrical charges that are not
moving. Electro – charges, statics–
not moving.
• Review chemistry
– Protons, positively charged, in
nucleus
– Neutrons, not charged, in nucleus
– Electrons, negatively charged ,
outside of nucleus
• Protons determine the identity of
the atom, and are not allowed to
move within the atom, they always
stay in the nucleus
Bonding
• There are 3 types of bonding
– Covalent = Sharing electrons
– Ionic = atoms steal or have their e- stolen
– Metallic = atom’s nucleus is in a “sea of electrons”
• No electron belongs to any particular nucleus
• All electrons interact with all protons in all of the nuclei
• This allows electrons to be “pushed” or pulled through
the material
Coulomb’s Law
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Coulomb’s Law
2nd Coulomb’s Law website
Which charges are which (challenge)
Move the charge where the force would be
zero
• Continue to work on this page
Coulomb’s Law
2
Nm
9
K = 9.0 X 10
C2
• Q is the charge of the object
• Charge is measured in the unit of Coulombs
(C)
• 1C is equal to the charge of 6.24 X 1018
electrons or protons
• d is the distance between the objects (we
don’t worry about if it is the center or the
surface)
Electric force compared to
Gravitational Force
• There are only 4 forces, the strong force, the
weak force, gravitational force and
electromagnetic force
• Physics also tells us that although it is pitifully
weak by comparison, gravity will predict the
outcome of the end of the Universe.
Electric force compared to
Gravitational Force
• In physics gravity
is by far the
weakest to all the
forces
Conductivity- Insulators
• The type of bond determines if an object will
be able to conduct electricity or not
– In covalent and ionic bonds the electrons are
shared between atoms and are tightly bound
– Electrons are not able to flow, these materials are
called insulators
– Examples?
Conductivity-conductors
• The type of bond determines if an object will
be able to conduct electricity or not
– In a metallic bond electrons are not tightly bound
and are able to flow. These materials are called
conductors.
– Conductor applet
– Examples?
Conductivity of dissolved Ionic
compounds
• Solid Ionic compounds themselves are not
conductors because their Ions are locked in place
• But when dissolved in water, or melt them they
become very good conductors because the ions
are now free to move about.
• Do demo
• Pure water is not a conductor of electricity and
neither are salts (sweat, dissolved minerals, sea
salts
• But put them together and watch out!
MORE
POSITIVE
Types of Charges
• There are 4 methods of
charging
• Friction
Objects likelihood of gaining
electrons can be summarized by
if they are “natural” or
“manmade”
The more natural tends to lose
electrons and become positive,
man made to gain electrons
and become negative
•Human Hands (if very dry)
•Leather
•Rabbit Fur
•Glass
•Human Hair
•Nylon
•Wool
•Fur
•Lead
•Silk
•Aluminum
•Paper
•Cotton
•Steel (neutral)
•Wood
•Amber
•Hard Rubber
•Nickel, Copper
•Brass, Silver
•Gold, Platinum
•Polyester
•Styrene (Styrofoam)
•Saran Wrap
•Polyurethane
•Polyethylene (scotch tape)
•Polypropylene Vinyl (PVC)
•Silicon
•Teflon
MORE
NEGATIVE
Types of Charges
• There are 4 methods of charging
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Friction
Induction
Conduction (animation to show friction and conduction charging)
And Polarization (applet to show how electrons move)
• Sweater Applet
Charges build up on points
• Keys
• Fingers
• Lightning rods
• This is because of something called an electric
field, it is kind of complicated.
Electric fields
• Electric fields can contain energy, the electric field diagram is just the way
of showing how much “potential” energy can be stored
• Electric fields diagrams are ways of visualizing the electric force that
Coulomb’s law predicts
• Electric fields can be drawn following a few rules
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All field lines start at a positive charge and end at a negative charge (if
there is one)
All field lines leave and enter the surface of the charged object at a right
angle to the surface
The “density” of the lines represents the strength of the electric field.
• A test charge is used to determine the force in an electric field
– It is a positive charge
– It should be thought of as having such a small charge that it doesn’t effect
the electric field in any way, but does predict the Coulomb’s force
• Applet with two unlike charges(with test charge)
• Applet with two like charges (with test charge)
• Applet where you can add charges
Lightning
• Lightning is a result of a built up static charge
between the ground and the clouds
• Lightning applet
• BrainPop on Lightning
Van de Graff Generator
Short video on how it works
Florescent light bulbs