Static electricity. Objectives Describe the historical development of the concepts of electrostatics. Identify examples of electric forces in everyday.

Static electricityStatic electricity

ObjectivesObjectives• Describe the historical development of the concepts

of electrostatics.

• Identify examples of electric forces in everyday life.

• Identify the two types of electric charge and how they interact.

AssessmentAssessment1. Name one of the founding fathers of the United States who

also contributed to our understanding of static electricity.

2. Describe two examples of electric forces in everyday life.

3. Which statement about electric forces is true?

AssessmentAssessment

A. A negative charge attracts a negative charge.

B. A positive charge repels a negative charge.

C. A negative charge repels a negative charge.

D. A positive charge attracts a positive charge.

Physics termsPhysics terms• static electricity

• electrostatics

• electric charge

• electrically neutral

• electric force

• electrostatic induction

• electroscope

Benjamin Franklin was America’s first famous scientist.

He and many others were studying the properties of static electricity even in the 1700’s.

•The study of electric charges at rest is called electrostatics.

•Static electricity results from a tiny excess of positive or negative electric charge on an object.

Static electricityStatic electricity

BrainstormBrainstorm

Where have you seen the effects of static electricity?

Think of a couple examples and share them with the student next to you.

An exampleAn exampleRub a balloon against a wool sweater.

This transfers some negative charges from the sweater to the balloon.

The sweater now has a net positive charge and the balloon has a net negative charge.

They will attract and stick together.

Shuffling your feet on the carpet can also transfer charges.

Touching a metal conductor, like a doorknob, causes the excess charge you’ve collected to be attracted to its opposite in the metal.

A tiny electric current flows … and that’s what makes the zap!

What makes the zap?What makes the zap?

Other everyday examplesOther everyday examplesClothes in a dryer without a dryer sheet make sparks.

A balloon rubbed on your hair sticks to the wall.

Open a package and the packing materials stick to your hands.

Pull a wool sweater over your head and your hair stands on end.

Electric chargeElectric chargeThere are two kinds of electric charge: positive (+) and negative (–).

Electric chargeElectric charge

In electrically neutral objects, positive (+) charges are balanced by an equal number of negative (–) charges.

There are two kinds of electric charge: positive (+) and negative (–).

There are two kinds of electric charge: positive (+) and negative (–).

Electric chargeElectric charge

In electrically neutral objects, positive (+) charges are balanced by an equal number of negative (–) charges.

Most objects are electrically neutral … otherwise there would be lightning everywhere all of the time!

As with magnetic poles, unlike charges attract:

Opposites attractOpposites attract

As with magnetic poles, unlike charges attract:

Like electric charges repel:

Opposites attractOpposites attract

As with magnetic poles, unlike charges attract:

Like electric charges repel:

Neutral particles feel no electric force at all from positive or negative charges.

Opposites attractOpposites attract

Electric forces of attraction and repulsion can be enormously strong.

These are the forces hold atoms and molecules together.

Electric forceElectric force

Electric forces of attraction and repulsion can be enormously strong.

These are the forces hold atoms and molecules together.

Electric forces are so strong that, outside of atoms, positive and negative charges are rarely separated for long!

Electric forceElectric force

The Van de Graaff generatorThe Van de Graaff generator

A Van de Graaff generator is a device that can separate electric charge.

Its sphere can reach thousands or even millions of volts, but it can only create a big spark – not a large electric current – if you touch it.

Charge distributionCharge distribution

If an object has a net charge, how are the excess charges distributed?

Charge distributionCharge distribution

Like charges repel, so charges will push each other apart as far as possible.

If the charges are on a Van de Graaff generator, repulsive forces will push them to the outside edge of the sphere.

Charge distributionCharge distribution

If the charges are on your head, the repulsive forces will push them out onto your hair, and push your hair apart!

Electrostatic inductionElectrostatic induction

It is also possible to charge an object without touching it.

Electrostatic inductionElectrostatic induction

It is also possible to charge an object without touching it.

Here, a negatively-charged rod repels negative charges and attracts positive charges. The sphere is now “charged”.

Electrostatic inductionElectrostatic induction

It is also possible to charge an object without touching it.

Here, a negatively-charged rod repels negative charges and attracts positive charges. The sphere is now “charged”.

This process of separating charge is called electrostatic induction.

Demo: electrostatic inductionDemo: electrostatic induction

Charge a plastic rod or ruler by rubbing it with wool.

Bring the rod close to an uncharged metal sphere or can. Is the metal object attracted to the rod?

Try it with other combinations of rods and materials.

Demo: the electroscopeDemo: the electroscopeAn electroscope uses induction to detect electric charge.

Summary: charging an objectSummary: charging an objectThere are three ways that objects typically become charged.

• conduction: A charged object contacts an uncharged object and transfers charges to it.

• conduction: A charged object contacts an uncharged object and transfers charges to it.

• friction: Different materials have different affinities for

charge. Rubbing these materials together causes charges to move transfer between the materials.

There are three ways that objects typically become charged.

Summary: charging an objectSummary: charging an object

• conduction: A charged object contacts an uncharged object and transfers charges to it.

• friction: Different materials have different affinities for

charge. Rubbing these materials together causes charges to transfer between the materials.

• electrostatic induction: A charged object is brought close to a neutral object, resulting in charge separation in the neutral object.

There are three ways that objects typically become charged.

Summary: charging an objectSummary: charging an object

1. Name one of the founding fathers of the United States who also contributed to our understanding of static electricity.

AssessmentAssessment

1. Name one of the founding fathers of the United States who also contributed to our understanding of static electricity.

AssessmentAssessment

Benjamin Franklin studied the properties of static electricity.

2. Describe two examples of electric forces in everyday life.

AssessmentAssessment

2. Describe two examples of electric forces in everyday life.

AssessmentAssessment

Answers could include lightning striking a tree, clothes in a dryer making sparks, a balloon rubbed on your hair sticking to the wall, packing materials sticking to your hands, etc.

3. Which statement about electric forces is true?

AssessmentAssessment

A. A negative charge attracts a negative charge.

B. A positive charge repels a negative charge.

C. A negative charge repels a negative charge.

D. A positive charge attracts a positive charge.

AssessmentAssessment3. Which statement about electric forces is true?

A. A negative charge attracts a negative charge.

B. A positive charge repels a negative charge.

C. A negative charge repels a negative charge.

D. A positive charge attracts a positive charge.