Physics lesson1 electricity&magnetism

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

(MORE ON THIS LATER)

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.

More on this later!

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.