physics lesson1 electricity&magnetism
TRANSCRIPT
ELECTRICITY AND MAGNETISM
Lesson 1
March 2 2012
Outline Review atomic structure. Define electricity Charges Static Electricity Friction Insulators and Conductors The Triboelectric Series Polarization Induction Conduction Grounding
Review – Parts of the AtomAtomic Particles
ProtonPositive charge
NeutronNo charge
ElectronNegative charge
Structure of the atom
Can you identify the particles?
“Electricity” – which particle does it sound like?
Electricity Electrons
Electricity is the MOVEMENT of electrons
Why Electrons?
Protons usually don’t moveThey are stuck in the nucleus with the
neutrons Electrons ORBIT around the nucleus
They can be moved out of their orbits, away from the nucleus
Charge
CHARGE is the measurement of EXTRA PROTONS or EXTRA ELECTRONS an object has.
A POSITIVELY CHARGED object has MORE PROTONS than electrons.
A NEGATIVELY CHARGED object has MORE ELECTRONS than protons.
Separating Charges
What do we mean when we say “separating charges?”
Remember: Electricity is the MOVEMENT of ELECTRONS
Separating Charges cont. Atoms usually have the same number of
PROTONS ( + positive charge) and ELECTRONS ( - negative charge)The positive and negative charges balance, so the
atom has a NEUTRAL CHARGE ADDING or REMOVING electrons changes the
charge of the atomADDING electrons makes the charge NEGATIVEREMOVING electrons makes the charge POSITIVE
This is what we mean when we say “separating charges.”
*A charged atom is called an ION
Separating Charges cont.How Do We Separate Charges?
How can we move electrons from one place to another?
FRICTION is one way to separate charge.What is FRICTION?
Separating Charges cont.Friction FRICTION is rubbing two objects together. When two objects are rubbed together,
some electrons move from one object to the other object.
This separates the charges of the atoms in the surfaces of the objects.
The surface of one object becomes POSITIVELY charged, and the surface of the other object becomes NEGATIVELY charged.
Static Electricity When electrons are moved from one object
to another object by friction, STATIC ELECTRICITY is the result
STATIC (adj) = stays in one spotOnce the charge has moved from one object to
the other, it stops moving.
Static Electricity cont.Insulators and Conductors
Materials like glass, plastic, rubber, and wood are good at collecting electrons in a static charge.These materials are called INSULATORS
Materials like metal and water are NOT good at collecting electrons in a static charge.These materials are called CONDUCTORS
Static Electricity cont.
Once electrons have been transferred from one object to another, we can say one object is POSITIVELY CHARGED and the other object is NEGATIVELY CHARGED.
What do OPPOSITELY CHARGED PARTICLES do?
LET’S FIND OUT!
Static Electricity cont.EXPERIMENT!
What does the balloon ATTRACT? What does it REPEL?
Static ElectricityExperiment Results The balloon was NEGATIVELY charged,
so it ATTRACTED anything with a POSITIVE charge
It REPELLED anything with a NEGATIVE charge.
This illustrates the LAW OF CHARGES!
Law of Charges
LIKE CHARGES REPELUNLIKE CHARGES
ATTRACT
…but what about neutral charges? Neutrally charged objects (objects with
no charge) are attracted to objects with POSITIVE and NEGATIVE charges.
The Triboelectric Series
Some materials are better at holding onto electrons, and some materials are better at giving away electrons.
The TRIBOELECTRIC SERIES ranks materials based on their affinity for electrons.
Triboelectric Series cont.
ALL materials fall somewhere on the triboelectric series.
Example using a few different materials:
Materials at the TOP of the list
gather more electrons than those
at the bottom.
Law of Conservation of Charge
Charge is only transferred. It just moves between objects.
Charge is not created from nothing,
and it is never destroyed.
Both the copper and the glass have NEUTRAL CHARGE.
They each have 6 units of electrons. What happens if you rub them together?
COPPER6e
GLASS6e
COPPER
8eGLASS
4e
Using the triboelectric series, we see that copper gathers more electrons than glass.
Using the Law of Conservation of Charge, we see that the total charge between the two stays the same.
2e
The glass loses 2 units of electrons, and so it now has a positive charge.
The copper gains those 2 units of electrons, and so it now has a negative charge.
Conductors and Insulators CONDUCTORS let electrons to flow easily
between atoms, or between molecules.
INSULATORS do not let electrons flow easily between atoms, or between molecules.
Can you remember some examples of conductors and insulators?
CONDUCTORSMetals, carbon, water, people?!
INSULATORSRubber, wood, glass
Conductors
When a charge is transferred to an object made from a conductive material, the charge spreads through the object.
Insulators
When a charge is transferred to an object made from an insulating material, the charge does not move.This is why insulators are good for
demonstrating static electricity. Static = does not move
Conductors vs. Insulators Conductors have an atomic structure
that lets electrons move in a clear path. Insulators have an atomic structure that
does not allow electrons to move in a clear path.
Polarization
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Polarization
Polarization means to separate into opposites.
When a charged object is placed on an oppositely charged (or neutrally charged) object, both objects will become polarized.
This means that their opposite sides will have opposite charges.