Electrostatics

A Short History ๏ Greeks ๏ Amber (ήλεκτρον) ๏ Rubbed with fur or cloth, it picks up dust & feathers ๏ Ben Franklin ๏ Concept of charge ๏ Extensive experiments ๏ Laws of Electrostatics ๏ Greeks ๏ Amber (ήλεκτρον) ๏ Rubbed with fur or cloth, it picks up dust & feathers ๏ Ben Franklin ๏ Concept of charge ๏ Extensive experiments ๏ Laws of Electrostatics

Types of Charge ๏ Positive ๏ Negative ๏ But think!! Where does charge come from?? ๏ Positive ๏ Negative ๏ But think!! Where does charge come from?? + + – –

๏ Your task: To rebuild an exact replica of the universe you must start with what particles?? ๏ Well, how would you build a simple atom? ๏ Your task: To rebuild an exact replica of the universe you must start with what particles?? ๏ Well, how would you build a simple atom? Review: Atomic Structure p p n n e–e– e–e– ๏ Nucleus ๏ Proton + ๏ Neutron ๏ Orbital ๏ Electron — ๏ Nucleus ๏ Proton + ๏ Neutron ๏ Orbital ๏ Electron —

IMPORTANT NOTE! ๏ All matter is made of atoms… ๏ therefore everything has charge. ๏ All matter is made of atoms… ๏ therefore everything has charge.

What About Neutral? ๏ NOT a type of charge ๏ DOES NOT mean no charge ๏ Means NO NET charge ๏ Equal + and — charges ๏ NOT a type of charge ๏ DOES NOT mean no charge ๏ Means NO NET charge ๏ Equal + and — charges – – – – – – – – = NO NET CHARGE NO NET CHARGE NEUTRAL

! Quick Quiz! ๏ A gold atom has 79 protons in its nucleus. ๏ How many electrons must it have to be neutral? 79 ๏ Yep! Electrons & protons have the same charge!

e–e– e–e– The Soul of Electricity ๏ Electrons ๏ Only atomic part free to move ๏ Electrons ๏ Only atomic part free to move NET—charge Electron Loss NET+charge Electron Gain

Conductors vs Insulators ๏ Conductor ๏ Conducts electron flow well and easily ๏ Accepts and gives away e – s easily ๏ Metals are best—lots of free outer e - s ๏ Conductor ๏ Conducts electron flow well and easily ๏ Accepts and gives away e – s easily ๏ Metals are best—lots of free outer e - s

Conductors vs Insulators ๏ Insulator ๏ Doesn’t conduct e - s well nor easily ๏ Conducts if e - s have enough energy ๏ Air, plastic, glass, styrofoam ๏ Insulator ๏ Doesn’t conduct e - s well nor easily ๏ Conducts if e - s have enough energy ๏ Air, plastic, glass, styrofoam

Detecting Charge ๏ Electroscope ๏ Detects charge and amount ๏ DOES NOT tell type

The Electroscope ๏ Needle moves in presence of charge ๏ Greater angle= greater charge ๏ Needle moves in opposite direction when opposite charge brought near

Franklin’s Four “Laws” ๏ “There are two types of charge— positive and negative.” ๏ “Like charges repel each other…” ๏ “…while opposite charges attract.” ๏ “A charged object will attract (or be attracted to) a neutral object.” ๏“๏“ There are two types of charge— positive and negative.” ๏“๏“ Like charges repel each other…” ๏“๏“ …while opposite charges attract.” ๏“๏“ A charged object will attract (or be attracted to) a neutral object.”

๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object Polarization – – – – –

๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object – – – –– – – – – – – –

Polarization ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object – – – –– – – – – – – –

Polarization ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object – – – –– – – – – – – –

Polarization ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object ๏ Happens when charged and neutral objects are brought near each other ๏ Electrons move within neutral object ๏ Temporarily charges opposite sides of neutral object – – – –– – – – – – – –

๏ The object is now POLARIZED ๏ Notice that the protons DO NOT move ๏ If the charged object is removed, the electrons will move back to their original locations ๏ The object is now POLARIZED ๏ Notice that the protons DO NOT move ๏ If the charged object is removed, the electrons will move back to their original locations Polarization – – – –– – – – – – – –

Three Methods of Charging CONTACTFRICTIONINDUCTION

CONTACT ๏ Charged object touches another ๏ Electrons move to balance themselves out ๏ Both objects end up with same charge

FRICTION ๏ Two objects rubbed together—one loses electrons to the other ๏ Triboelectric series Triboelectric series Triboelectric series ๏ Objects end up with opposite charges

INDUCTION ๏ Multiple step procedure: 1)Bring charged object near neutral (Polarize) Ground the neutral object Ground the neutral object Remove charged objectRemove charged object

INDUCTION ๏ Grounding allows electrons to flow into/out of “neutral” object ๏ Objects end up with opposite charges

QUESTIONS ??