ELECTRICITY

TYPES OF ELECTRICITY

Electricity is the study of how charges interact. In general, electricity refers to electric charge.

There are two types of electricity:

static electricity and current electricity.

How Electricity was discovered!Discovered by Thales (a Greek philosopher) in 600 B.C.

Thales observed that a piece of amber rubbed with cat fur could attract small pieces of straw and wood shavings. By rubbing the amber and the fur, Thales had created an electric charge on both objects (one positive, the other negative.).

Coincidentally, the Greek word for amber is “elektron”.

Because the charge does not leave the material, it is said to be stationary or static. This led to the term static electricity.

STATIC ELECTRICITY

Electric charge is a property of the particles of atoms. Recall the structure of the atom, from chemistry:

PROTON,Positive charge, high mass

Electric Charge

ELECTRON,Negative charge, low mass

NUCLEUS

NEUTRON, Neutral charge, high mass

BOHR-RUTHERFORD MODEL OF A LITHIUM ATOM

SIMPLIFIED MODELS OF A LITHIUM ATOM

Simplified Model of Atom used in this Class!

THIS IS NOT A BOHR-RUTHERFORD DIAGRAM OF AN ATOM! THIS IS A SIMPLIFIED DIAGRAM OF AN ATOM TO HELP EXPLAIN STATIC ELECTRICITY FOR OUR LESSON.

Electric Charge of an AtomElectrons can be added to, or removed from atoms.http://library.thinkquest.org/27961/guide/4%20-%20high/elect/2%20-%20moving%20electrons.html

Neutrally Charged Lithium

Atom

Negatively Charged Lithium

Atom

Positively Charged Lithium

Atom

Symbols used for charges

+NEUTRAL CHARGE

ATOM, (MAY NOT BE

SHOWN ON A DIAGRAM)

POSITIVELY CHARGE ATOM

NEGATIVELY CHARGED ATOM

DO NOT CONFUSE “+” AS THE PROTONS IN A NUCLEUS, THE NUCLEUS REMAINS IN ITS SAME POSITION INSIDE AN ATOM IN A OBJECT !

Another Example of Electric Charge of an Atom

.

Neutrally Charged

Aluminum Atom

Negatively Charged

Aluminum Atom

Positively Charged

Aluminum Atom

DRAW A SIMPLIFIED ATOMIC MODEL FOR NEUTRAL, NEGATIVE AND POSTIVE CHARGED ATOMS OF CARBON, C AND MAGNESIUM, Mg.

Charges on ObjectsNeutral objects have equal numbers of protons and

electrons within a quantity of matter.

Charges on ObjectsNegatively charged objects have more electrons than protons.

Notice there are more neutrally charge atoms than negatively charged atoms! How can this object be negatively charged?

Charges on ObjectsPositively charged objects have fewer electrons than protons.

Notice there is a negatively charged atom in this object!

Is this object really positively charged?

Draw the charges for this object

What is the overall charge on this object?

What are the overall charges of these objects?

Static electricity is an imbalance of electric charge of an object. Often charges move to the surface of an object.

REMEMBER! “+” is a positively charged atom, not a proton.

The nucleus of an atom always stays in the same position and electrons move from atom to atom!

Static Electricity

When two different materials come in contact, electrons can be transferred between them,

causing an imbalance in charge.

Static Electricity

Charging by friction occurs when two neutral objects made of different materials rub against or touch each other and electrons are transferred between them.

BEFORE

Charging by Friction (contact i)

fur

Plastic rod

The rod and fur are both neutral.

DURING

Charging by Friction

fur

Plastic rod

Charging by FrictionNotice that some of the electrons from the fur moved to the plastic rod and thus changed the number of charges on the rod and fur.

AFTER•What are the new charges on each object?

•Are there still the same number of “atoms” in each object?

•Are there still the same number of

+ , - and 0 charges from before we rubbed the rod and fur?

Electrostatic Series• When objects are charged by friction, one material is more

likely to accept electrons, while the other is more likely to give up electrons; this is because some kinds of atoms are more strongly attracted to electrons than others.

• The electrostatic series is a list that ranks the tendency of different materials to gain electrons. It can be used to predict the charge that will be gained by two objects (made from different materials) when they come in contact..

• An electrostatic series chart is arranged in terms of the relative “hold” that different materials have on their electrons.

Human Skin

+(weaker tendency

to gain electrons)

(stronger tendency to gain electrons)

-

Rabbit Fur

Acetate

Glass

Human Hair

Nylon

Wool

Cat fur

Silk

Paper

Cotton

Wood

Amber

Rubber Balloon

Vinyl

Polyester

Ebonite

Charging by conduction occurs when two objects with different amounts of electric charge come in contact and electrons are transferred from on object to the other.

BEFORE

Charging an object through Conduction(contact ii)

Metal rod-overall -5

charge

Metal ball- overall neutral charge

During

Charging an object through Contact or Conduction

Metal rod

Metal ball

•Metal rod losing 5 electrons.

•Metals ball gaining 5 electrons

Charging an object through Contact or Conduction

AFTER•What are the new charges on each object?

•Are there still the same number of “atoms” in each object?

Metal ball

Metal rod

A neutral object is charged by conduction when a charged object touches it. The neutral object becomes charged with the same charge as the object it touched.

More about Charging by Conduction

When two charged objects with different amounts of electric charge come in contact, electrons are transferred between them.

metal rod x- overall +3 charge metal rod Y- overall charge +1

metal rod x- gaining an electron, metal rod Y- losing an electron

metal rod x- overall +2 charge metal rod Y- overall charge +2

Most materials let electrons flow through them, though some let electrons flow more easily than others.

A conductor is any material that will allow the flow of charge (i.e. electrons). Electrons distribute themselves evenly throughout the object (ex. metals, solutions).

An insulator is any material that does NOT allow the flow of charge. Electrons are not free to move, causing a build-up of charge in a part of the object (ex. rubber, glass, paper).

Classifying materials by their Electrical Characteristics : Conductors & Insulators

What are conductors used for?

• Conductors are used whenever a flow of electricity is needed.

• The inside of a wire, the tips of batteries, and the rods of a plug are conductors.

• Copper and aluminum are the most common materials used due to their low cost and efficiency.

See Table 9.1, pg 308 of text

What are Insulators used for?

• Rubber is an excellent insulator, and it is used to protect people from electricity.

• Insulators are used primarily for safety.

• Common uses include gloves for working on power lines and the main body of a plug.

See Table 9.1, pg 308 of text

GroundingObjects with excess electric charge-either positive or negative- can have access charge removed by a process called grounding.

When we ground an object, we transfer electrons between the object and a large neutral object such as Earth (the ground).

Symbol used for grounding

electrons

electrons

Grounding

Before the discharge, the hand is negatively charged and the faucet is neutral

During discharge, excess electrons are transferred from the hand into the ground.

After discharge, the negative charge on the hand has been removed.

Induction – placing a charged object near a neutral object without touching it. The neutral object will end up with a temporary charge opposite of the

charged object.

Charging an Object through Induction

Neutral sphere grounded Separation of Charge by bringing

a charged rod close by

Charging an Object through Induction

Keep the charged rod near sphere and remove

connection to ground.

Remove the charged rod

THE LAW OF ELECTRIC CHARGE

Opposite charges attract (law of attraction) Positive, + and Negative,-

Same charges repel (law of repulsion) Positive, + and Positive, + or

Negative, – and Negative, –

Neutral and charged objects attract Neutral,0 and Positive, + or

Neutral,0 and Negative, –

Neutral and Neutral objects do nothing!

Detecting Charge: The ElectroscopeAn electroscope can be used to detect the presence of an electric charge.

Static Electricity:Applications & Phenomena

• Lightning• Photocopying Machine• Painting with charges• Gasoline Truck• Electrostatic Precipitator• Appliances

Sections 9.3-9.4 of Textbook