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•Electrostatics

is the study

of electric

charge at

rest. 2

What Is Static Electricity?

• A stationary electrical charge that is built up

on the surface of a material

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Read Intro of Handout

• Charged Versus Uncharged Objects:

Compare number of e- to number of p+

• Positively-Charged

• Negatively-Charged

• Uncharged (neutral)

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p+ > e-

e- > p+

p+ = e-

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1) Contains Positive and Negative charges

2) The Negative charges moved to the top b/c they’re

attracted to the Positive bar.

3) The Positive Arm repels.

++++++++++++++

Don’t let electrons travel thru

Examples:

Wood

Plastic

Paper

Rubber

Grass

Let electrons travel thru

Examples:

Water

Metals: Cu, Al, Au

Salt Water

Alloy

Graphite

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q/Q Coulomb (C)

Electrons -1.6 x 10-19 C

Protons +1.6 x 10-19 C

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1C x 1e-/-1.6 x 10-19 = 6.25 x 1018 e-

Electrons transfer.

Electrons are the only ones

that can move.

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CHARGE BY FRICTION

PhET Sweater

Drag your

feet on the

carpet.

Rub balloon

on your

hair.

Electrons

are

transferred

from one

material to

another.

When a balloon rubs a piece of wool...

– electrons are pulled from

the wool to the balloon.

The balloon has more

electrons than usual.

+

+

+

+

+

–––––

The balloon: – charged,

The wool: +charged

wool

CHARGING BY FRICTION:

Rubbing materials does NOT create electric charges.

It just transfers electrons from one material to

the other.

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A balloon when rubbed on your

head becomes charged by picking

up extra electrons from your hair.

That same balloon, because it is

charged, will attract a neutral

object like pieces of paper.

-+

-

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CHARGE BY CONDUCTION

Requires

CONTACT.

Electrons transfer.

Both are left

Negative.

Charged object

touches a neutral

sphere.

During rubbing, what have been

transferred between the woolen cloth

and the balloon?

A Electrons B Protons

C Neutrons

A balloon has a negative charge when rubbed by woolen cloth.

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CHARGE BY INDUCTION

Negative object

moves near a

neutral sphere.

Just move close

to it – no contact.

Requires

grounding.

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If the balloon can attract some paper

scraps, which of the following cannot

be the charge of paper scraps?

A Neutral B Positive

C Negative

A balloon has a negative charge when rubbed by a woollen cloth.

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• In conducting objects, they are so loosely bound

that they may be induced into moving from one

portion of the object to another portion of the

object. To get an electron in a conducting object

to get up and go, all that must be done is to place a

charged object nearby the conducting object.

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CHARGE BY POLARIZATION

What effects will a charged balloon have on:*When Negative

Charge gets near the

e- freely move away

(repel) causing a

positive side to

attract

*Neutral particles

line up – once

polarized then the

can sticks.

*So the stream of

water attracts

*Can-Charged

Negative Balloon

to Pop Can

*Wall-Charged

Negative Balloon

to Paper

*Water- Water is

Polar

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In the context of electricity, polarization is the process of separating opposite charges within an object. The positive charge becomes separated from the negative charge. By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge. Charge becomes separated into opposites.

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Repulsion will be greatest for those electrons nearest negatively charged

balloon. Mass migration of electrons from balloon's side of aluminum can towards

the opposite side of the can. This electron movement leaves atoms on balloon's side

of can with shortage of electrons; they become positively charged.

Atoms on side opposite of can have an excess of electrons; they become negatively

charged. Two sides of aluminum pop can have opposite charges. Overall can is

electrically neutral; positive and negative charge has been separated from each

other. Charge in the can has been polarized.

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Grounding

• Removing the excess

charge on an object by

means of the transfer of

electrons between it and

another object of

substantial size.

• Example: Touch a door

handle and get shocked.

• Works because excess

electrons find each other

repulsive and forces them

to look for a way of

separating from each

other.

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Grounding

If the object has a positive charge...

Similarly, if the object has a negative charge...

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• Static Electricity Video

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Which drawing shows the field around a single positive charge?

2. Which drawing shows the field around a single negative charge?

3. Which drawing shows an attraction?

4. Which drawing shows a repulsion?

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