General Physics 2

Ancient Greeks (600 BC)

discovered static charge when they observed amber rubbed with wool.

Ancient Greeks (600 BC)

They found that amber, when rubbed, became electrified and attracted pieces of straw or feathers.

Thales of Miletus

The 1st recorded investigator was in Ancient Greeks

“Electricity”

comes from the Greek word Elektron meaning “amber.”

Elektron

meaning “amber”

William Gilbert (1600)

Found that electrification was not limited to amber

William Gilbert (1600)

Found out that many other substances when rubbed against another have this ability of amber.

‘Electrics’

Found out that many other substances when rubbed against another have this ability of amber, which he called this substance ______

Charles Coulomb (1785)

Created a device that helped him develop his theories on charges and electric force and field.

Charles Coulomb (1785)

Confirmed the inverse square relationship of electrical forces.

Benjamin Franklin (1752)

Credited with being the first to discover that lightning and thunder are the result of electrical charges.

Hans Oersted (1820)

Compass needle deflects when placed near an electrical current.

Michael Faraday

A wire moved near a magnet, an electric current is observed in the wire

James Clerk Maxwell (1865-1873)

Formulated the laws of electromagnetism

Hertz

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Verified Maxwell’s equations

Electricity

is the name given to a wide range of electrical phenomena, such as:

* lightning
* spark when we strike a match
* what holds atoms together.

Electrostatics

involves electric charges:

* the forces between them,
* the aura that surrounds them, and
* their behavior in materials.

Electrostatic

is a study on the electric charges in the static or steady state condition.

Static Electricity

is the result of an imbalance between negative and positive charges in an object.

Static Electricity

these charges can build up on the surface of an object until they find a way to be released or discharged.

Static Electricity

rubbing certain materials against one another can transfer negative charges, or electrons.

Electrostatics

is the study of electric charge at rest

Electric charge

is a fundamental property of matter.

• Positive Charge

• Negative Charge

2 Types of Electric Charges:

All ordinary matter is made of atoms, and all atoms contain charged particles.

Where does charge come from?

Protons

the atomic nucleus contains positively-charged _______.

Electrons

found outside of the nucleus, tiny fast-moving, negatively charged particles.

Atoms

fundamental building blocks of the matter

Protons

positive electric charges

Protons

repel positives, but attract negatives

Electrons

negative electric charges

Electrons

repel negatives, but attract positives

Neutrons

neutral electric charge

Neutrons

has the same amount of protons and electrons

atom

Every ______ is composed of a positively charged nucleus surrounded by negatively charged electrons.

electrons

Each of the _______ in any atom has the same quantity of negative charge and the same mass.

Protons and neutrons

compose the nucleus

Protons

about 1800 times more massive than electrons, but each one carries an amount of positive charge equal to the negative charge of electrons.

1800

Protons are about ____ times more massive than electrons, but each one carries an amount of positive charge equal to the negative charge of electrons.

Neutrons

have slightly more mass than protons and have no net charge.

Neutral

Atoms usually have as many electrons as protons, so the atom has zero net charge

* Positive ion
* Negative ion

An Atom may gain or lose electron forming IONS:

Positive ion

atom losing one or more electrons has positive net charge.

Negative ion

atom gaining one or more electrons has negative net charge.

*Coulomb* abbreviated as *C*

the SI unit of charge is the __________

Electronic charge

the electron and proton both have the same charge, with the electron being negative and the proton being positive, this amount of charge is often called ___________

Positive Ion

Neutral atom – electron =

Negative Ion

Neutral atom + electron =

Electrons - outermost

attracted loosely and can be easily dislodged

Electrons - innermost

attracted very strongly to oppositely charged atomic nucleus

* In any charging process, no electrons are created or destroyed.
* Electrons are simply transferred from one material to another.
* One body acquires a positive charge and the other acquires an equal but negative charge.

Conservation of Electrical Charge

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1. Friction
2. Contact
3. Induction

An object becomes electrostatically charged by:

Friction

which transfers electrons between two objects in contact

Contact

with a charged body which results in the transfer of electrons

Induction

which produces a charge redistribution of electrons in a material

Triboelectric series

is a list that ranks materials according to their tendency to gain or lose electrons.

Triboelectric Charging

the process of electron transfer as a result of two objects coming into contact with one another and then separating

Conductor

Materials in which one or more of the electrons in the outer shell of its atoms are not anchored to the nuclei of particular atoms but are free to wander in the material

Conductor

Materials through which electric charge can flow are called ___________.

Conductor

Metals are good _______________for the motion of electric charges because their electrons are “loose.”

Metals

are good conductors for the motion of electric charges because their electrons are “loose.”

Conductor

Example: Metals such as copper and aluminum

Insulators

Materials in which electrons are tightly bound and belong to particular atoms and are not free to wander about among other atoms in the material.

Insulators

These materials, known as insulators, are poor conductors of electricity.

Insulators

Example: Rubber, glass, mica, paper, glass

Semiconductors

Are materials that can be made to behave sometimes as insulators and sometimes as conductors.

Semiconductors

Fall in the middle range of electrical resistivity between insulators and conductors

Semiconductors

They are insulators when they are in their pure state

Semiconductors

They are conductors when they have impurities.

Conduction and Induction

There are two ways by which a neutral body may be charged:

Conduction

is charging by contact between the neutral body and the charging body

Conduction

charging by contact and friction

Conduction

electrons are being transferred by friction when one material rubs against another. For example, stroking cats fur, combing your hair, rubbing your shoes on a carpet.

Conduction

electrons transfer from one material to another by simply touching. For example, when a negatively charged rod is placed in contact with a neutral object, some electrons will move to the neutral object.

Induction

if a charged object is brought near a conducting surface, even without physical contact, electrons will move in the conducting surface.

Induction

Charging by _____can be illustrated using two insulated metal spheres.

single noncharged conductor

Uncharged insulated metal spheres touching each other, in effect, form a ________________________________

Induction

When a negatively charged rod is held near one sphere, electrons in the metal are repelled by the rod.

Induction

The excess negative charge has moved to the other sphere, leaving the first sphere with an excess positive charge.

Induction

They have been charged by _______, which is the charging of an object without direct contact.

grounding

Charge induction by _______ can be illustrated using a metal sphere hanging from a nonconducting string.

Induction

The charge on the spheres has been redistributed, or induced.

When the spheres are separated and the rod removed, the spheres are charged equally and oppositely.

grounding

When we allow charges to move off (or onto) a conductor by touching it, we are __________ it.

thunderstorms

Charging by induction occurs during

Coulomb’s Law

mathematical formula to calculate the electrostatic force vector between two charged particles and was named after the French physicist Charles Coulomb.

Coulomb’s Law

states that the electrical force between charged particles is proportional to the quantity of each of the charges and inversely proportional to the square of the distance between them.

the force is repelling

if the charges are alike in sign

the force is attractive

if the charges are not alike,

Coulomb’s Law

similar to Newton’s law of gravitation for masses

Coulomb’s Law

underlies the bonding forces between molecules

Coulomb’s Law

the force between point charges is proportional to the product of the charges, divided by the square of the distance between them.

Electrostatic Force

also called Coulomb’s force

Electrostatic Force

is defined as the amount and direction of attraction or repulsion between two charged bodies.

Electric Charge

is an attribute that is fundamental as mass, electric current, and amount of substance.

Electric Charge

it is measured in Coulomb (C).

Electric Charge

this should not be confused with electric current which is the flow of electric charge per time, measured in ampere (A)

Coulomb (C)

the unit of electric charge in honor of Charles-Augustin de Coulomb (1736-1806).

Charles-Augustin de Coulomb (1736-1806)

was a French physicist who made the first accurate measurements of electric force between charges.

Fe = electrostatic force (N)

ke = Coulomb constant = 9.0×109 Nm2 /C2

q1 = electric charge of object 1 (C)

q2 = electric charge of object 2 (C)

r = distance between the two objects (m)

Coulomb’s law quantifies the electric force:

where:

It depends on the magnitude of each charge, and the distance between them. You need to shorten the distance.

How can you increase the repulsive force between two positive charges? What does this force depend on?